Are Deep Sand Beds, DSBs, dangerous to use in a marine aquarium?

[Reefin' Dude]

what numbers do you have that allows you to dismiss it as insignificant when that dead horse we keep beating dies,

I take dead fish out of the tank. If you do not, perhaps that is why you need to vacuum the substrate.

I am, as it happens, an expert on phosphate metabolism. I've studied it for more than 20 years, and have invented products that sell more than a billion dollars worth each year correcting hyperphosphatemia in people.

There is a flow chart in this link which shows the relative excretion of phosphate in urine (which is almost totally inorganic phosphate) and in feces (which is a combination of organic and inorganic phosphate).

https://www.inkling.com/read/medica...-2nd/chapter-52/calcium-and-phosphate-balance

The inorganic phosphate in urine excretion dominates, even if you ignore all of the inorganic phosphate in the feces. Then you seem to assume that all of that feces ends up in the substrate, which is utterly untrue. Other macroscopic creatures eat it, sometimes over and over. I had a kole tang that loved to eat my yellow tangs feces as fast as it came out. That drops the original phosphate ending up in feces by another factor of, say, based on the data above, three. Each cycle drops it significantly.

At the end of the day, yes, there obviously is phosphate making it to the substrate (as I've agreed along), but it is not the dominant player in phosphate balance in a reef tank.

it is not the soluble inorganic P from the excretion that i am arguing about. as you have said earlier this is relatively easy to take care of. i have agreed with this from the beginning. it is the solid organic matter that is point i am trying to get at.

yes, we all remove dead fish when we see them, but that can not be done with the benthic organisms, or the solid waste products from the benthic organisms. or for that matter any of the fish that we miss that may have died. this all contain organic P. the more of this material the more decomposition occurs resulting in more soluble iP.

if P makes it into the substrate, then how is this not a P sink? that is all i have been saying all along. a substrate collects P. it was not there in the beginning, now it is. the more organism, the more P there must be in the substrate.

How can you assume it's reactive?

Or even organic for that matter?

For all we know a lot of those particulates could be mineral precipitates, bits of sediment or rock that were eroded off, etc; that's what the vast, vast majority of marine sediments are. As far as I know, there is absolutely zero analysis of the makeup of the particles that build up, so we can't really rule out the possibility that it isn't organic.

If it actually is organic, the very fact that it's still there after all this time is pretty strong evidence that it is difficult or even impossible for the organisms in the tank to use that "muck". Useable organic material is scavenged very effectively and quickly except under the most extreme cases (heavy sedimentation etc.) that don't take place in an aquarium. Eventually, after being recycled over and over, all the usable organic material is stripped out, and what's left is essentially inert and unusable to all but very select and specialized microbes. Marine sediments in nature are full of such highly-processed refractory compounds that essentially are never used, but this represents a tiny fraction of the organic material that moves through the system. We don't know this for sure, but I'd be willing to wager (and in a sense do wager my systems' health) on those particulates being the unwanted and unusable leftovers produced by a healthy ecosystem. Waste, after all, constitutes what an organism cannot use, so eventually so much is stripped out that all that's left is functionally inert.

Organic matter consumption takes place over the course of MINUTES in a healthy system, breaking it down into the soluble components that can either re-enter the food chain or be removed through our variety of filtering mechanisms. What's left after that process is what accumulates. Does it contain organic carbon, nitrogen, and phosphorus? Almost certainly yes, but it almost equally certainly exists in practically unusable forms. Based on that, I would even argue that focusing on removing detritus is going to miss most of the reactive material unless it's removed from the system on at least a daily basis; otherwise you're focusing on removing something that - from the perspective of the food web - was already removed.

if it is inert, then why would we want it in the substrate? if it is inert, then what are the benthic organisms eating? wouldn't over time the substrate get deeper because of this increase in inert material? if it inert, then why do people tend to get algae blooms after a substrate has been disturbed?

Here's a paper that studied the release of phosphate from a fish on a coral reef.

http://m.aslo.net/lo/toc/vol_30/issue_1/0146.pdf

It shows that for these fish, the production each day was

1.49 + 0.45 pmol g-l d-l for MRP (a measure of dissolved inorganic phosphate)
2.01 + 0.34 for TDP, (a measure of dissolved inorganic and organic phosphate)
4.54 t- 2.30 for particulate P. (includes both inorganic and organic phosphate that is stuck to a particle somehow)

They also show that fecal pellets lost 55%of their phosphate by leaching inorganic phosphate within 24 h, and before significant bacterial growth had taken place in the pellet. The pellets were then stable for 5 days until bacterial growth began to become significant.

So of the phosphate released by these fish each day, only 31% remained in their feces after 24 h.

good to know. the more organisms there are in the system the higher the amount of P in the system from their feces. do you have a rate of release for this last 31%? the more feces then the more of this 31% is going to be available over time as it decomposes. unless the rate of release of this 31% is faster than the production of feces by all of the organisms in the system. if not, then there is going to be a net gain in P from the feces for the entire system. correct?

It absolutely could if it is indeed bacterial cells, though of course that's a big question mark; even if it's refractory compounds rather than organisms, it still almost certainly contains P, though how much you'd remove by pulling that out relative to other removal methods is anyone's guess without some hard data. As far as the second question, Randy certainly could give you a better answer as far as the specific chemistry of phosphates binding to other minerals, but on a broader scale of organic matter in sediments, one of the really interesting "hot topics" in the field right now is the idea of "protection" (for lack of a better term) of organic molecules. According to this theory, organic molecules that would otherwise be labile and rapidly used are protected within the abiotic structure of the sediment (think of a small organic molecule stuck in a deep crevice of the crystalline structure that no microbe can fit in). If that actually happens in nature (and that's an "if" right now, though it is a plausible idea and there is some evidence supporting it), then there's no reason that couldn't function the same way in the aquarium and act as a natural sequestration for later removal or a sink in and of itself. It's also a lot more likely with crystalline sediments like carbonate than with clays etc that tend to be rounder at the ultra-microscopic level, so that's a very real but unexplored fate for P.

didn't the skimmer study show that the majority of organic P was from the bacteria? why wouldn't this be occurring all over the system? not just in the water column, but also in the substrate. why would the bacteria care? as long as they have resources they are happy campers, correct? if these bacteria are in the substrate, then how are they going to get into the water column to be removed by a skimmer unless the substrate is disturbed?

our systems are bacterial driven. they are doing all of the heavy lifting.

G~

 

[Randy Holmes-Farley]

good to know. the more organisms there are in the system the higher the amount of P in the system from their feces. do you have a rate of release for this last 31%? the more feces then the more of this 31% is going to be available over time as it decomposes. unless the rate of release of this 31% is faster than the production of feces by all of the organisms in the system. if not, then there is going to be a net gain in P from the feces for the entire system. correct?

Sure, there will be some gain from degradation of feces in the substrate, and substantially more from direct release of phosphate from organisms that eat fish food or process the feces before it gets into the substrate.

 

[Amphiprionocellaris]

it is not the soluble inorganic P from the excretion that i am arguing about. as you have said earlier this is relatively easy to take care of. i have agreed with this from the beginning. it is the solid organic matter that is point i am trying to get at.

yes, we all remove dead fish when we see them, but that can not be done with the benthic organisms, or the solid waste products from the benthic organisms. or for that matter any of the fish that we miss that may have died. this all contain organic P. the more of this material the more decomposition occurs resulting in more soluble iP.

if P makes it into the substrate, then how is this not a P sink? that is all i have been saying all along. a substrate collects P. it was not there in the beginning, now it is. the more organism, the more P there must be in the substrate.

Frankly, so what?

The more corals/fish/anemones/crabs/etc etc you have, the more P you have, by definition. If more P is being put in than is being removed via the various filtration, the system is growing, which most tanks are, and there's no problem; if it is at steady state, then the P input through food matches the removal through all the different methods, and there's no problem. It's a simple mass balance. By definition, a sink is removal; if P travels to the substrate but then is released back into the water column, the sediment IS NOT a sink. If there was no phosphate in the sediment to begin with, and some ends up in there, then indeed some has accumulated, by definition. But you are suggesting that this accumulation continues forever, without any evidence to show that it doesn't reach a steady state, or that the trace accumulation of refractory P is a problem down the road. In the first months, my tanks always accumulate a 1 - 2 mm thick layer of whitish particles in the sump and about ~5ish mm of it in the sediment, but after that I never see an increase.

It's not really that the points you are making are incorrect, it's that the conclusions you seem to jump to based on them aren't necessarily supported. You act as if organic, solid P traveling to the sediment then being processed to soluble P is a bad thing despite the fact that 1) the system needs that energy flow to support things we want, like coral growth (this is relevant http://onlinelibrary.wiley.com/doi/10.1111/gcb.12566/full) and 2) we have a variety of means in place to strip out and remove that soluble P as it's produced.

if it is inert, then why would we want it in the substrate? if it is inert, then what are the benthic organisms eating? wouldn't over time the substrate get deeper because of this increase in inert material? if it inert, then why do people tend to get algae blooms after a substrate has been disturbed?

If it's inert, there's no harm in it, so why bother removing it? If it's inert, the benthic organisms by definition are eating something else, like fresh organic matter being delivered to the sediment or recycled in the surficial sediment; we are talking about highly dynamic systems with lots of nutrient flow going on at all times; what little sediment accumulates is the tiny fraction of what's moving that no one wants. And the algae blooms - if they even happen; I never get them in my tank and my large clams can definitely cause some sand storms - are more likely from the nitrogen that is present in significant amounts in the sediment. Nitrification is a relatively slow process, so there's usually a standing pool of it at the interface between the oxic and anoxic zones; add to this that nitrogen is almost always the limiting nutrient in marine environments, and any sudden algae blooms are more likely due to a sudden influx of nitrogen, not P. Though you are certainly right, over the course of decades to centuries the sediment would get deeper due to the accumulation of that matter, just as it does in the ocean.

didn't the skimmer study show that the majority of organic P was from the bacteria? why wouldn't this be occurring all over the system? not just in the water column, but also in the substrate. why would the bacteria care? as long as they have resources they are happy campers, correct? if these bacteria are in the substrate, then how are they going to get into the water column to be removed by a skimmer unless the substrate is disturbed?

I'm not sure what you are referring to as the "it" that occurs all over the system, but saltwater is heavily populated by an ambient bacterial population well over a million cells/mL and the nutrient cycling does occur throughout the tank. More of it just tends to happen in the sediment due to the larger bacterial populations per volume. Beyond that, I'm not sure what your point is...why do we need them to leave the sediment and get into the water column? Any P that is contained within them will be broken down and recycled either into another organism's biomass or released into the water and removed from there. And please note that I've said throughout that discussion that we essentially have no idea what those particulates are, and that they MIGHT be bacteria, but it's anyone's guess.

 

[Reefin' Dude]

good to know. the more organisms there are in the system the higher the amount of P in the system from their feces. do you have a rate of release for this last 31%? the more feces then the more of this 31% is going to be available over time as it decomposes. unless the rate of release of this 31% is faster than the production of feces by all of the organisms in the system. if not, then there is going to be a net gain in P from the feces for the entire system. correct?

Sure, there will be some gain from degradation of feces in the substrate, and substantially more from direct release of phosphate from organisms that eat fish food or process the feces before it gets into the substrate.

how does the benthic organism feces, or even the dead benthic organisms get out of the substrate?

wouldn't these other organisms eating this increased processing also increase the amount of feces getting into the system, if new food is added? how does this not keep increasing the total amount of P in the system, and increase the amount of soluble iP in the water column? doesn't this equate to needing more GFO, resins, carbon dollollies to remove the soluble iP?

G~

 

[Amphiprionocellaris]

how does the benthic organism feces, or even the dead benthic organisms get out of the substrate?

wouldn't these other organisms eating this increased processing also increase the amount of feces getting into the system, if new food is added? how does this not keep increasing the total amount of P in the system, and increase the amount of soluble iP in the water column? doesn't this equate to needing more GFO, resins, carbon dollollies to remove the soluble iP?

G~

They get removed by being broken down into their soluble components, which then diffuse or are advected out of the sediment into the water column. Presumably, the organisms responsible for this process do indeed consume some of it into new biomass, and excrete the rest as soluble waste P (which is what directly enters the water column to be removed) or waste solid P (which is in turn broken down through the same processes). The P that has been taken up as biomass is sequestered until the organism in question dies in some way, in which case it enters the cycle again as the solid organic P that is broken down, again producing solid and soluble components that are either recycled or removed.

The rate of P addition to the system is solely determined by the amount of addition via food. If we have the system set up with an excess of exports, ie. the rate of removal via filtration or growth is limited by how much there is to remove rather than being limited by the media's intrinsic removal rate, then there would be no net change because import is balanced by export. When you add incorporation into biomass, which is necessary for a full mass balance, then the total amount of P is increasing, just like the total amount of C, O, N, Ca, etc is increasing. The system is not at steady state, and is not designed to be, if we want our organisms to grow. At some point, feeding more and more, yes, you would need to add a larger amount of resin or GFO, or just replace it more often, but the net effect, and what we're after, is minimizing the pool of dissolved P by using aggressive export (both biological and abiotically).

 

[asylumdown]

how does the benthic organism feces, or even the dead benthic organisms get out of the substrate?

wouldn't these other organisms eating this increased processing also increase the amount of feces getting into the system, if new food is added? how does this not keep increasing the total amount of P in the system, and increase the amount of soluble iP in the water column? doesn't this equate to needing more GFO, resins, carbon dollollies to remove the soluble iP?

G~

You cannot have more phosphorous in the system than you add to it. The amount of P you need to remove via resins is proportionate to the rate you add it, so you if you do not want to require more resin and carbon 'dollollies', keep fewer fish or put the ones you've got on a diet. Whether that P goes straight to your skimmer and resins in a bare bottom tank (though I think you're underestimating the amount of biological activity going on in your rocks...), or spends several months/years working it's way through your sand-bed, you cannot require more export than you import, which is controlled by the amount you add.

Who cares if the total P in the system increases forever in the form of biomass and an ever expanding food web if your equipment keeps the amount that does return to the water column as reactive inorganic phosphate nearly undetectable? You're not going to require more and more resin to keep it under control, you're going to require an amount of resin that is equivalent to the net fraction your tank doesn't use over time. On a tank with a sand bed, that might mean hardly any resin up front as all the P gets taken up in the substrate and an ever expanding microbial and faunal food web, and more later on as your tank reaches some sort of saturation point (if such a thing is possible) and more of the P you add in the form of food day to day winds up in the water column as reactive inorganic P, but over time you'll still only ever require the amount of resin necessary to soak up the balance between what you have added and what your tank uses or exports via other means such as skimming, water changes, etc.

Whether you have a sand bed or not, that is still true. Which is why most people who run bare bottom tanks still use GFO.

 

[asylumdown]

They get removed by being broken down into their soluble components, which then diffuse or are advected out of the sediment into the water column. Presumably, the organisms responsible for this process do indeed consume some of it into new biomass, and excrete the rest as soluble waste P (which is what directly enters the water column to be removed) or waste solid P (which is in turn broken down through the same processes). The P that has been taken up as biomass is sequestered until the organism in question dies in some way, in which case it enters the cycle again as the solid organic P that is broken down, again producing solid and soluble components that are either recycled or removed.

The rate of P addition to the system is solely determined by the amount of addition via food. If we have the system set up with an excess of exports, ie. the rate of removal via filtration or growth is limited by how much there is to remove rather than being limited by the media's intrinsic removal rate, then there would be no net change because import is balanced by export. When you add incorporation into biomass, which is necessary for a full mass balance, then the total amount of P is increasing, just like the total amount of C, O, N, Ca, etc is increasing. The system is not at steady state, and is not designed to be, if we want our organisms to grow. At some point, feeding more and more, yes, you would need to add a larger amount of resin or GFO, or just replace it more often, but the net effect, and what we're after, is minimizing the pool of dissolved P by using aggressive export (both biological and abiotically).

+1 What he said...

 

[Reefin' Dude]

You cannot have more phosphorous in the system than you add to it. The amount of P you need to remove via resins is proportionate to the rate you add it, so you if you do not want to require more resin and carbon 'dollollies', keep fewer fish or put the ones you've got on a diet. Whether that P goes straight to your skimmer and resins in a bare bottom tank (though I think you're underestimating the amount of biological activity going on in your rocks...), or spends several months/years working it's way through your sand-bed, you cannot require more export than you import, which is controlled by the amount you add.

not if what is being said about the decomposition rate of feces is true. there is 31% of feces that is not removed in 24 hours from all of the animal organisms in the system. if more food is coming in than this 31% being produced, then the total amount of P in the system is ever increasing.

Who cares if the total P in the system increases forever in the form of biomass and an ever expanding food web if your equipment keeps the amount that does return to the water column as reactive inorganic phosphate nearly undetectable? You're not going to require more and more resin to keep it under control, you're going to require an amount of resin that is equivalent to the net fraction your tank doesn't use over time. On a tank with a sand bed, that might mean hardly any resin up front as all the P gets taken up in the substrate and an ever expanding microbial and faunal food web, and more later on as your tank reaches some sort of saturation point (if such a thing is possible) and more of the P you add in the form of food day to day winds up in the water column as reactive inorganic P, but over time you'll still only ever require the amount of resin necessary to soak up the balance between what you have added and what your tank uses or exports via other means such as skimming, water changes, etc.

Whether you have a sand bed or not, that is still true. Which is why most people who run bare bottom tanks still use GFO.

at some point the population will crash. the organisms will run out of resources. this could be food or it could be space. the resources are not unlimited.

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so, what came first, the benthic organisms or the organically bound P within the substrate in which they feed on?

G~

 

[Amphiprionocellaris]

not if what is being said about the decomposition rate of feces is true. there is 31% of feces that is not removed in 24 hours from all of the animal organisms in the system. if more food is coming in than this 31% being produced, then the total amount of P in the system is ever increasing.

No, because yesterday's 31% has now been decomposed into soluble components and removed, to be replaced by today's 31%. An over-simplification, of course, but the point is that the 31% or whatever proportion that is not broken down immediately over the first whatever time period does not simply suddenly become inert. What is happening at any instantaneous moment in the tank is a balance of *multiple* processes over *multiple* time scales, including the immediate breakdown of freshly produced organic matter as well as the breakdown of older material. The *only* way that non-biological P (ie. P not sequestered in living organisms, soluble inorganic P is probably a good proxy for this) increases with feeding is if there is insufficient removal via filtration. Otherwise there is a violation of mass balance.

at some point the population will crash. the organisms will run out of resources. this could be food or it could be space. the resources are not unlimited.

Not really. What is missing here is the population biology concept of carrying capacity. At some point, and I'm not sure this ever happens in an aquarium in terms of bacteria or even small macrofauna, the population will reach the level at which available resources is sufficient only to maintain rather than grow the current population. At his point, recycling of the resource due to death is balanced by consumption due to growth. If there is a downward shift in the availability of this resource, then the population will decrease to the new capacity, and vice versa if there is an increase. As an example, if insufficient organic material is supplied to the benthic community (e.g. if it is removed before it can be recycled), then this carrying capacity would be very low and there wouldn't be very many fauna in the sand bed, which could then cause lots of problems in terms especially of nitrogen cycling. I use this example specifically because in systems with limited food input, the gradual decline in nutrient levels due to removal can potentially lead to collapse of the sand bed and loss of function (possibly one thing causing "old tank syndrome") to what is almost a barren sand bed more analogous to abyssal sediments. But in a system with appropriate feeding, the population will tend towards equilibrium over time.

so, what came first, the benthic organisms or the organically bound P within the substrate in which they feed on?

G~

Both. The system evolves holistically over time as it is established, and population levels and nutrients both increase hand in hand. That's the basic premise behind cycling and establishing a tank. The typical pattern is of course that nutrient levels go up first, because the population simply takes time to grow. That's also the basic principle of habitat succession, and why it takes multiple months for a tank to truly stabilize and even longer for it to reach maturity.

 

[asylumdown]

Are Deep Sand Beds, DSBs, dangerous to use in a marine aquarium?

not if what is being said about the decomposition rate of feces is true. there is 31% of feces that is not removed in 24 hours from all of the animal organisms in the system. if more food is coming in than this 31% being produced, then the total amount of P in the system is ever increasing.

What Randy stated was that most P in feces had leached out of it in 24 hours, not the fraction left over was forever unavailable to export. That remaking fraction will get consumed, digested, recycled, and at some point will end up in the water in a form GFO or skimming can remove.

at some point the population will crash. the organisms will run out of resources. this could be food or it could be space. the resources are not unlimited.

Huh? What evidence do you have that such a thing happens or is a risk day to day? What you're describing is a system crash, in which case phosphate export is the least if your worries. Yes, your micro faunal population might become limited by space, at which point your tank is close to a steady state from that perspective. But you still only need to export the fraction your tank doesn't use day to day, whether that amount goes up because there's no more room for worms, or you never had the worms in the first place is kind of irrelevant and it's true for both bare bottom and sand bed tanks. It's still controlled by your rate of input, which is dependent on the amount you feed your tank every day.

If my sand bed suddenly reduces it's rate of phosphate consumption or sequestration and I have to use more GFO, then so what? If I had no sand bed it wouldn't consume or sequester any phosphate, so I'd need to export that much or more anyway. It's the rate of input that drives all of this. It's not the sand bed's fault or problem I'm keeping a tank full of obese, over fed fish.



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so, what came first, the benthic organisms or the organically bound P within the substrate in which they feed on?



G~

Does it matter? Where's the beginning of a circle, and why should anyone care?

 

[Reefin' Dude]

What Randy stated was that most P in feces had leached out of it in 24 hours, not the fraction left over was forever unavailable to export. That remaking fraction will get consumed, digested, recycled, and at some point will end up in the water in a form GFO or skimming can remove.

no it doesn't. what you suggest is like saying that an organism is not going to expel any wastes until all of the P has been taken out of the system. that remaking fraction again equals an increase in total P by biomass. yet another increase in waste expelled. lets say that the remaining 31% is a 3/4 life equation. it is going to take several days for all of that P to be converted into a form that will be removed by iP conversion or binding through GFO. that is any feces that is not directly ingested by another organism. if it is ingested into another organism, then this P could going to be a part of another 31% needing to be decomposed.

Huh? What evidence do you have that such a thing happens or is a risk day to day? What you're describing is a system crash, in which case phosphate export is the least if your worries. Yes, your micro faunal population might become limited by space, at which point your tank is close to a steady state from that perspective. But you still only need to export the fraction your tank doesn't use day to day, whether that amount goes up because there's no more room for worms, or you never had the worms in the first place is kind of irrelevant and it's true for both bare bottom and sand bed tanks. It's still controlled by your rate of input, which is dependent on the amount you feed your tank every day.

basic biology. i am not sure where the confusion is. why do we carbon dose? because C is becoming limited. what if space becomes limited by all of these benthic organisms, what happens to the population? the substrate can only hold so many organisms space wise and only so many food wise. there has to be a limit. when that limit is reached what happens to the remaining food supply that goes uneaten? it is now able to sit and just decompose at that 31% rate.

If my sand bed suddenly reduces it's rate of phosphate consumption or sequestration and I have to use more GFO, then so what? If I had no sand bed it wouldn't consume or sequester any phosphate, so I'd need to export that much or more anyway. It's the rate of input that drives all of this. It's not the sand bed's fault or problem I'm keeping a tank full of obese, over fed fish.

again, it doesn't matter if you have a substrate or not. at some point all of the P that has gone into the system will need to be exported. it is the rate of export that drives all of this, not input. it is far easier to input than output. our systems are not designed for export, but sequestering. that is all i am saying.

you are right it is not the substrate that is the fault or the problem, it is the aquarist. the substrate is doing what it does best. hide detritus. keeps it all nice and happy. just keeping poo as a pet. the longer the poo is allowed to be kept as a pet, the more of that 31% is allowed to get back into the water column.

Does it matter? Where's the beginning of a circle, and why should anyone care?

it matters greatly. it defines in which direction the P is traveling. there must be some of that 31% poo in the substrate in a great enough amount to support the given ecosystem in the substrate. the ecosystem could not be in the substrate without these resources. if the substrate goes in clean, then somehow this organic P is getting in there to support the ecosystem. how? it is either through the release of iP from the PSB's, or from the accumulation of organically bound P from above working its way downward through the substrate.

G~

 

[Amphiprionocellaris]

no it doesn't. what you suggest is like saying that an organism is not going to expel any wastes until all of the P has been taken out of the system. that remaking fraction again equals an increase in total P by biomass. yet another increase in waste expelled. lets say that the remaining 31% is a 3/4 life equation. it is going to take several days for all of that P to be converted into a form that will be removed by iP conversion or binding through GFO. that is any feces that is not directly ingested by another organism. if it is ingested into another organism, then this P could going to be a part of another 31% needing to be decomposed.

What makes you say this? The 31% is what is leached out abiotically, not what is a product of decomposition. Randy made no statement whatsoever about what happens to that remaining fraction after that, though I'd be willing to bet that he could give a very detailed rundown of the P's fate. But it doesn't matter how long the P remains in the pool if the pool size is kept low via export. Say you're brewing beer; you start one keg each day, and you drink a keg each day (I wouldn't recommend this). Regardless of whether it takes 20 days or 20 minutes to brew a keg, the net is the same: one in and one out. The exact same thing happens in nutrient cycles; at steady state, it doesn't matter how long it takes a particular atom of P to be removed because new input is balanced by new output regardless of the age of the P being removed. If the system isn't at steady state - which we've already establish it isn't in a healthy aquarium - then slightly less is being exported than is being imported, and that excess is supporting new growth (a sequestration). You could probably manipulate the system such that the proportion being exported goes up, but it would be at the cost of growth unless made up for with additional input.

basic biology. i am not sure where the confusion is. why do we carbon dose? because C is becoming limited. what if space becomes limited by all of these benthic organisms, what happens to the population? the substrate can only hold so many organisms space wise and only so many food wise. there has to be a limit. when that limit is reached what happens to the remaining food supply that goes uneaten? it is now able to sit and just decompose at that 31% rate.

We dose carbon to make up for the carbon that is lost to Co2 through respiration, or in the case of nitrogen cycling, to provide carbon for use in denitrification. If it does become limited and we don't dose more, then the system would reach an equilibrium based on the carrying capacity. Same goes for space, nitrogen, or any other finite resource, and when that limit is reached the population stays steady; it does not decline (unless it has overshot the limit, which leads to damped oscillation and return to equilibrium). The population does not need to grow to recycle nutrients, and the only thing that would change is that the arrow going into biomass drops and instead shifts to export. You are focusing on one number from one process, but that ignores the basic ecology of the tank.

again, it doesn't matter if you have a substrate or not. at some point all of the P that has gone into the system will need to be exported. it is the rate of export that drives all of this, not input. it is far easier to input than output. our systems are not designed for export, but sequestering. that is all i am saying.

If you remove all of the P that has gone into the system, you will end up with an empty glass box. And you cannot isolate import and export when considering the change in P pools, because you need to know both in order to know the net export. And frankly, your statement that our systems are designed for sequestration is a gross overstatement. Most of the people on this forum probably use a multitude of natural and artificial export mechanisms specifically to enhance that term. Unless of course you mean that our systems are designed to encourage growth, in which case that's absolutely true.

you are right it is not the substrate that is the fault or the problem, it is the aquarist. the substrate is doing what it does best. hide detritus. keeps it all nice and happy. just keeping poo as a pet. the longer the poo is allowed to be kept as a pet, the more of that 31% is allowed to get back into the water column.

That's not what a functioning sand bed does. Plain and simple. It no more hides detritus and keeps poo as a pet than does coral. You've said this whole set of statements multiple times and it's no more true now than it was the first time.

it matters greatly. it defines in which direction the P is traveling. there must be some of that 31% poo in the substrate in a great enough amount to support the given ecosystem in the substrate. the ecosystem could not be in the substrate without these resources. if the substrate goes in clean, then somehow this organic P is getting in there to support the ecosystem. how? it is either through the release of iP from the PSB's, or from the accumulation of organically bound P from above working its way downward through the substrate.

It goes in during the initial cycling and establishment of the tank, along with all the nitrogen, carbon, calcium and various other elements necessary for a functioning system. But again, your assumption that it starts accumulating and never stops is just wrong. That's why no one in their right mind treats a brand new tank the same as a mature one. And then once all the nutrients go in, the sand bed system reaches an equilibrium based on the balance of input and output processes, and that's that. In the long-run functioning of the tank, it does not matter that in the first few weeks there is a net movement of nutrients into the sand bed; there is also a net movement of nutrients into corals and fish over the entire life time of a system.

 

[Reefin' Dude]

What makes you say this? The 31% is what is leached out abiotically, not what is a product of decomposition. Randy made no statement whatsoever about what happens to that remaining fraction after that, though I'd be willing to bet that he could give a very detailed rundown of the P's fate. But it doesn't matter how long the P remains in the pool if the pool size is kept low via export. Say you're brewing beer; you start one keg each day, and you drink a keg each day (I wouldn't recommend this). Regardless of whether it takes 20 days or 20 minutes to brew a keg, the net is the same: one in and one out. The exact same thing happens in nutrient cycles; at steady state, it doesn't matter how long it takes a particular atom of P to be removed because new input is balanced by new output regardless of the age of the P being removed. If the system isn't at steady state - which we've already establish it isn't in a healthy aquarium - then slightly less is being exported than is being imported, and that excess is supporting new growth (a sequestration). You could probably manipulate the system such that the proportion being exported goes up, but it would be at the cost of growth unless made up for with additional input.

irrelevant as to how it leaches back out. the point is that it is time delayed. more is coming in faster than it can get out. organisms are always expelling waste. the tank is getting fed faster than all of the poo can go away, the greater the amount of animals the longer it takes for the P to get converted. sequestering is still not exporting. i thought i made that clear several pages back. recycling is not exporting. if more is coming in, and there are more biomass, there must be more poo for the organisms to eat. keeping poo as a pet in order to feed these other organisms. which in turn supply more poo.

lets take you keg example. where are the resources coming for that first keg? now are you ****ing into another keg to supply the resources for your next keg of beer? when do you start brewing the next keg, when the other one is gone or before so that you do not run out? are the organisms in the take waiting for their next meal or is it already there? if he population is increasing, then there must be available resources for the organisms to brew their next keg.

We dose carbon to make up for the carbon that is lost to Co2 through respiration, or in the case of nitrogen cycling, to provide carbon for use in denitrification. If it does become limited and we don't dose more, then the system would reach an equilibrium based on the carrying capacity. Same goes for space, nitrogen, or any other finite resource, and when that limit is reached the population stays steady; it does not decline (unless it has overshot the limit, which leads to damped oscillation and return to equilibrium). The population does not need to grow to recycle nutrients, and the only thing that would change is that the arrow going into biomass drops and instead shifts to export. You are focusing on one number from one process, but that ignores the basic ecology of the tank.

the population must grow in order to sequester more and more of a given resource. if it is not sequestering, then it must be available. more resources needed to remove it now that it is in soluble iP form. what happens when somebody adds to much carbon when carbon dosing? how is this not cause a crash of another organism because of resource hogging? how can it reach a steady state if more and more food is coming in, and all of those benthic organisms are still there pooing and dying. it takes time, even if it is minutes or hours, it doesn't matter. there is a time delay in the release back into the system.

If you remove all of the P that has gone into the system, you will end up with an empty glass box. And you cannot isolate import and export when considering the change in P pools, because you need to know both in order to know the net export. And frankly, your statement that our systems are designed for sequestration is a gross overstatement. Most of the people on this forum probably use a multitude of natural and artificial export mechanisms specifically to enhance that term. Unless of course you mean that our systems are designed to encourage growth, in which case that's absolutely true.

not at all. you are just supplying the food necessary for the given organisms. you do not need to supply the resources for all of those organisms necessary for the decomposition of the poo of your must have organisms. as long as that must have organisms has its beer it is happy. it could not care less if it has to wait for it to poo, then grow the hops, then grind it, then mash, then water yadda yadda yadda. it doesn't need all of that. it just needs the beer and someplace to use the restroom so it is not swimming in its own ****. i thought we went through this earlier.

That's not what a functioning sand bed does. Plain and simple. It no more hides detritus and keeps poo as a pet than does coral. You've said this whole set of statements multiple times and it's no more true now than it was the first time.

then please tell me how a functioning sand bed works. what is all of that poo doing in the substrate if it is not kept as a pet in order to feed other organisms? i am feeding the corals directly along with the fish. i am also cleaning up after them with every water change and running the skimmer 24/7. i am pulling everything unnecessary out. it is very true. you all have proven it many times. there must be organically bound P as a food source to support an animal. you all are saying that the excrement is the food source for all of these organisms. you are therefore keeping the poo around as a pet to feed these other organisms. what else is it doing there?

It goes in during the initial cycling and establishment of the tank, along with all the nitrogen, carbon, calcium and various other elements necessary for a functioning system. But again, your assumption that it starts accumulating and never stops is just wrong. That's why no one in their right mind treats a brand new tank the same as a mature one. And then once all the nutrients go in, the sand bed system reaches an equilibrium based on the balance of input and output processes, and that's that. In the long-run functioning of the tank, it does not matter that in the first few weeks there is a net movement of nutrients into the sand bed; there is also a net movement of nutrients into corals and fish over the entire life time of a system.

why not? why does it matter how old the tank is? that is the point i am trying to make. if you just feed the resources and pull out the wastes necessary for the must have organism, then why would the maintenance change over time? what can change? you are in complete control of the inputs and exports. think of it as going to the store for food for the house. you can either go every day and get the food for the day, or hit a big super store and get large quantities and store them for later. you are in control of the inputs. as for the outputs. feel free to not empty the trash or flush the toilet. you can either keep it around or not. in our household we tend to remove it as soon as we are done.

you are right it does reach an equilibrium, when the substrate becomes full of material. whether it is sequestered in some magic non reactive form or in a reactive form. it is still going into the substrate. at some point is must reach a point where it can not accept any more, or any more an be converted in to the magic non-reactive form.

again. all i am saying is just siphon out the substrate on a regular basis. it could be every year, every week, or even every few years. it just needs to be done in order for it to remain functioning. there has to be movement of material in order for all of the organisms to remain viable. every now and then you must cull the herd in order to maintain a healthy population.

just pick the maintenance schedule you can live with and see how it goes. if more resources are needed to maintain the given nutrient levels you are wanting, then just siphon out all of that grey/brown fluffy stuff in between all of those grains. the benthic organisms will be back in short order. doing this restarts all of the sequestering of the P accumulating in the substrate.

G~

 

[billsreef]

our systems are not designed for export, but sequestering. that is all i am saying.

If I design a system with protien skimmers, refugium (with chaeto) or algae scrubber, GFO, and of course water changes....how is export not designed into the system

Note: sand beds or not are quite irrelevant for this.

 

[Reefin' Dude]

you are supplying nutrients to support organisms that are not your must have organisms.

if your must have organisms are worms and other benthic organisms, then all is good. that is your goal. if your must have organisms is a pelagic fish or a coral, than all of these extra organisms running around represent accumulated nutrients not necessary for the health of the must have organism.

are you spreading your waste around the house in order to create an entire ecosystem? why not? if you want to keep dung beetles, then you might.

G~

 

[Amphiprionocellaris]

irrelevant as to how it leaches back out. the point is that it is time delayed. more is coming in faster than it can get out. organisms are always expelling waste. the tank is getting fed faster than all of the poo can go away, the greater the amount of animals the longer it takes for the P to get converted. sequestering is still not exporting. i thought i made that clear several pages back. recycling is not exporting. if more is coming in, and there are more biomass, there must be more poo for the organisms to eat. keeping poo as a pet in order to feed these other organisms. which in turn supply more poo.

"More is coming in faster than it can get out". Baseless statement with zero evidence behind it. Not true in a properly established tank.

"The tank is getting fed faster than all of the poo can go away" Another baseless statement with zero evidence.

"The greater amount of poo the the longer it takes for the P to get converted". Simply not true because the higher load of animals that supposedly leads to that poo also processes it more quickly.

No one said sequestration is exporting. But coral growth is a form of sequestration, so if you're going to argue that sequestration is a bad thing, better ditch your corals.

No one said recycling is exporting. Recycling returns nutrients including phosphorus back into the water column so that they CAN get exported. The system will increase in biomass over time if it is healthy; if it is not increasing, it is not healthy. I don't understand why growth of an ecosystem is a bad thing, and you should probably let the whole of ecology know about that one, too.

No more "poo" can be running through the system than is input. Done. End of story. If there is more biomass recycling that "poo", so what? What matters to corals are soluble reactive phosphates (SRP, which is what a P test actually measures). The goal is to balance the input with the export, and that's exactly why we use resins, GFOs, algal turf scrubbers, and on down the line.

lets take you keg example. where are the resources coming for that first keg? now are you ****ing into another keg to supply the resources for your next keg of beer? when do you start brewing the next keg, when the other one is gone or before so that you do not run out? are the organisms in the take waiting for their next meal or is it already there? if he population is increasing, then there must be available resources for the organisms to brew their next keg.

What?

This statement leads me to believe you didn't understand the point of the keg analogy at all. I wasn't discussing where the resources come from (but that would be food in this scenario), I was illustrating that if your input matches your output, the total pool will not change regardless of how big the pool is and how long it takes something to travel through the pool. You argue that because it takes time for all of a particular input to be removed, it must be increasing, but I wanted to illustrate that in reality it doesn't matter how long it takes if the input/output is balanced. That's a basic concept of food webs and ecology. Though you are right that an increasing population does indeed require resources, again another basic concept of ecology. But that has nothing to do with net import, flux balancing, and steady states.

the population must grow in order to sequester more and more of a given resource. if it is not sequestering, then it must be available. more resources needed to remove it now that it is in soluble iP form. what happens when somebody adds to much carbon when carbon dosing? how is this not cause a crash of another organism because of resource hogging? how can it reach a steady state if more and more food is coming in, and all of those benthic organisms are still there pooing and dying. it takes time, even if it is minutes or hours, it doesn't matter. there is a time delay in the release back into the system.

I'm starting to get lost here, because there are a bunch of distantly related concepts being thrown out here. Yes, growth is a sequestration, so growth is required to sequester something. And yes, if it's not being sequestered, then it's available for removal. The resources you mention for removal are ones we already use, again the resins, GFO, and skimming. That's part of designing a system for export. Again, these statements are all mostly true, but so what? Why, specifically, does it matter if more soluble reactive phosphate is produced to be removed by our filtration mechanisms instead of being sequestered in new growth?

As far as the overdosing of carbon, it would lead to a decrease in the oxygen penetration depth, increased CO2 production, and increased rates of denitrification, and possibly sulfide production if it's way overdosed. But that's a completely different topic regardless.

Steady state, by definition, is a state whereby the population is not changing. If you feed the same amount, and keep your resins and GFO's properly replaced, then steady state will be reached at the point where the population reaches its carrying capacity based on the standing pool of SRP (which will likely be low). Hopefully, while feeding, you also have nutrient export mechanisms in place; otherwise you're going to see an increase in the pool size, and should probably run some sort of filtration to enhance export.

not at all. you are just supplying the food necessary for the given organisms. you do not need to supply the resources for all of those organisms necessary for the decomposition of the poo of your must have organisms. as long as that must have organisms has its beer it is happy. it could not care less if it has to wait for it to poo, then grow the hops, then grind it, then mash, then water yadda yadda yadda. it doesn't need all of that. it just needs the beer and someplace to use the restroom so it is not swimming in its own ****. i thought we went through this earlier.

No the "must have organism" doesn't care how it gets what it needs. But doing all of that (recycling, processing, export, etc, as opposed to direct removal before it can enter the food chain) IS NOT harmful to the tank, as you imply. So to follow the analogy (which I now hesitate to do, because I have a feeling it's not going to emerge in the same way as I wrote it), you don't need to homebrew your beer, but some people like to, and they should know the details of it and that it's no worse than buying your beer premade. And personally, I prefer to have my system set up in such a way that the whole system deals with most of it and I only have to intervene occasionally for water changes and dosing.

I did not once ever say that a sand bed is necessary or the only way to e.g. keep a healthy coral.

then please tell me how a functioning sand bed works. what is all of that poo doing in the substrate if it is not kept as a pet in order to feed other organisms? i am feeding the corals directly along with the fish. i am also cleaning up after them with every water change and running the skimmer 24/7. i am pulling everything unnecessary out. it is very true. you all have proven it many times. there must be organically bound P as a food source to support an animal. you all are saying that the excrement is the food source for all of these organisms. you are therefore keeping the poo around as a pet to feed these other organisms. what else is it doing there?

Please re read all of the posts on this because I don't really have the inclination at this point to re-type everything I've explained, because I'm not convinced it's been effective. But I'll at least give a basic rundown. The sand bed as a whole processes and recycles the organic matter that comes to it, leading both to nutrients flowing up the food chain and being broken down into soluble components that can then be removed. The "poo", does not stay around long; it is processed very quickly, and re enters the food chain as nutrients necessary for growth. This is all balanced by removal of especially the SRP, so that in a mature system, all input is removed with the exception of the small percentage that is used to support new biomass.

why not? why does it matter how old the tank is? that is the point i am trying to make. if you just feed the resources and pull out the wastes necessary for the must have organism, then why would the maintenance change over time? what can change? you are in complete control of the inputs and exports. think of it as going to the store for food for the house. you can either go every day and get the food for the day, or hit a big super store and get large quantities and store them for later. you are in control of the inputs. as for the outputs. feel free to not empty the trash or flush the toilet. you can either keep it around or not. in our household we tend to remove it as soon as we are done.

Because over time, the bacterial and macrofaunal populations reach their respective carrying capacities and equilibria. That takes time to happen, and it will happen regardless of how you set your tank up unless it consists of a glass box with corals and fish only. At that point of maturity, the change will be minimal, but up to then, the dynamics are stabilizing and populations are reaching maturity, and so the energy and nutrient budgets are continually shifting (towards the equilibrium values) until stability is reached.

you are right it does reach an equilibrium, when the substrate becomes full of material. whether it is sequestered in some magic non reactive form or in a reactive form. it is still going into the substrate. at some point is must reach a point where it can not accept any more, or any more an be converted in to the magic non-reactive form.

It reaches equilibrium when the input matches the output, which has absolutely nothing to do with the pool size (ie. the sediment being "full"). It can absolutely accept more with a concurrent change in population size as the carrying capacity changes. That's how an ecological equilibrium works.

again. all i am saying is just siphon out the substrate on a regular basis. it could be every year, every week, or even every few years.

Not disagreeing you can do that if you want. It won't cause harm unless you rely on the benthic macrofaunal community for denitrification.

it just needs to be done in order for it to remain functioning. there has to be movement of material in order for all of the organisms to remain viable. every now and then you must cull the herd in order to maintain a healthy population.

Nope.

That's my whole point. It does NOT need to be done for the sand bed to remain functioning. The movement of material is provided by the natural recycling of elements that takes place, with removal being balanced by fresh input from the aquarist. You absolutely do NOT need to "cull the herd" with the benthos. It reaches a carrying capacity and stays there unless the supply of nutrients is diminished through lack of feeding or suddenly new filtration.

just pick the maintenance schedule you can live with and see how it goes. if more resources are needed to maintain the given nutrient levels you are wanting, then just siphon out all of that grey/brown fluffy stuff in between all of those grains. the benthic organisms will be back in short order. doing this restarts all of the sequestering of the P accumulating in the substrate.

Or let the benthos do its thing and use resins, GFO, skimming, etc remove the excess SRP. This is one of my big problems: the approach you advocate is not a blanket approach, it's not suitable for everyone, and it's not the only way to go about having a healthy reef.

My regime: Weekly water changes of 10%, purigen and carbon, skimming, a healthy sand bed, ridiculous amounts of plankton and pellet food feeding, and I have never once detected nitrate or phosphate. I bet you could poll 100 different aquarists and get 100 different maintenance regimes, and I'd bet that the majority of them are very successful.

 

[Nano sapiens]

Setting aside the argument of whether detritus is mostly inert, or not, the physical aspects of this material are at least equally important, IMO. Out in the open, such as in a bare sump where water can flow in, over and around, the material is not much of an obstruction and does little harm. However, in a sand bed or in live rock an excess of detritus impedes advective flow and thereby diminishes the rate at which substances reach the bacteria. If allowed to continue and escalate, the end result is obvious as the bacteria become less and less efficient at processing/reducing/converting (ammonium, nitrite, nitrate, phosphate, etc.) and the top tier organisms begin to suffer due to water quality degradation.

Nowhere is this more apparent as in a Pico or Nano tank with the relatively large ratio of organisms to water volume. Typically, in nano tanks where the substrate is not disturbed (and the detritus is not removed), they will function properly for 8 months to 1-1/2 years before the system has some major issues resulting in many of the higher life forms in distress or dying or, quite often, a total system crash.

On the topic of substrate, I have found that it is virtually impossible to vacuum the life out of it. I vacuum my shallow 1" substrate frequently and deeply 2x/week with my water changes and in between I can still see worm tracks up against the glass.

 

[Amphiprionocellaris]

Setting aside the argument of whether detritus is mostly inert, or not, the physical aspects of this material are at least equally important, IMO. Out in the open, such as in a bare sump where water can flow in, over and around, the material is not much of an obstruction and does little harm. However, in a sand bed or in live rock an excess of detritusl impedes advective flow and thereby diminishes the rate at which substances reach the bacteria. If allowed to continue and escalate, the end result is obvious as the bacteria become less and less efficient at processing/reducing/converting (ammonium, nitrite, nitrate, phosphate, etc.) and the top tier organisms begin to suffer due to water quality degradation.

I think this is a super, super important point, and I'm glad you brought it up, because that's one of the big open-ended questions: how quickly does it take the sediment to clog? This is something that (I bet anyone who's been following this thread can predict my next words...) we simply don't know yet, and it really is something hugely important that advocates of sand bed methodologies (such as myself) need to address. I would argue based on my experience that clogging doesn't take place over the tens of years our aquaria run, based on my experience (but again, the plural of anecdote is not data), but this is honestly something that really requires more study. I think you bring to the table some very important examples with nano and pico aquaria, because those are going to experience the same-magnitude process rates, but the percentage impact will be much larger. Aquarists who are keeping those systems must honestly be very careful to consider the import-export rates of major nutrients, because even a slight imbalance over even small time scales will have a huge impact.

If permeability changes through the accumulation of small particles, then as you say, advective flow could be dramatically decreased, which would then decrease the ability of the benthic community to do the nutrient processing we use it for. This could be one source of the old tank syndrome, and also one reason mature tanks start to unexpectedly see algae growth. In a diffusion-dominated environment (and it is really open-ended how we should consider our systems; and it's possible that it's entirely situation-dependent), this is less the case, because permeability does not play a role in diffusion. At the same time, some organisms responsible for advection actually demonstrate the ability to respond to and even alter the permeability of their domain by moving such small particles to be removed by mechanical export! How much that occurs in the aquarium is of course anyone's guess (and it really is a guess until we secure a source of funding for actual aquarium science), but this whole topic is hugely important and really needs more investigation. I am a staunch proponent of sand bed methodologies as one way to lead to a successful reef tank, but I will absolutely and completely say that sediment clogging is one major open question we need to address as support for our method(s). And this idea has so many unknown aspects to it that the questions and ideas for experimentation grow almost exponentially!!!

Please pardon my wild speculation and exuberance on this topic, and I apologize if I throw concepts and terms out without proper explanation; this particular subject is what I've been studying for my PhD and so ideas and hypotheses can proliferate wildly when I talk about them! (but on that note, to anyone observing this thread, please ask if we throw out unfamiliar concepts or terms...the reason RC exists is first and foremost to educate). These sorts of unanswered questions are where the real scientific and hobby progress happens!

 

[Nano sapiens]

I think you bring to the table some very important examples with nano and pico aquaria, because those are going to experience the same-magnitude process rates, but the percentage impact will be much larger. Aquarists who are keeping those systems must honestly be very careful to consider the import-export rates of major nutrients, because even a slight imbalance over even small time scales will have a huge impact.

I am one of the small nano keepers (by choice) these days working with ~10g total water volume, but I've kept larger SW fish and reef systems over the last 30 years or so. Keeping a nano functioning optimally over the long haul has it's own set of unique challenges and you are correct that striking a optimal input-output balance is a sensitive balancing act. Loosing that balance is relatively easy and getting it back again can be quite the challenge.

 

[Paul B]

There are a number of people who have posted their long term success with deep sand beds without this cesspool effect you keep talking about.

I am far to stupid to get into these conversations and that graph that was posted gave me a headache so I know I do everything wrong, but what are we considering long term success? Is that like 5 or 10 years? If it is, that's almost the life span of a hermit crab.
A hermit crab who smokes.