Deep Sand Bed -- Anatomy & Terminology

[tmz]

For clarification; no ammonia was dosed as noted earlier by another poster

. Food and live animals were used to provide nutrients in this experiment.

This is from the study:

We prepared homogenized squid (Loligo sp.) pellets for food as described in Pawlik et al. (1995). Fish were fed ad libitum each week day (unfed on weekends) until they did not ingest the final pellet offered to them. The final uneaten pellet was left in the aquarium to provide food for scavengers in the tank

This is a point of emphasis because , I think it's important to represent the study accurately .

The other criticisms of the study noted above may/may not have weight and folks can form their own opinion on them.
I for one have never heard of a 6 square foot minimum ; don't know what it means in terms of tank size or sand volume or how it is relevant.

For those who wish to read it the second article/study, it is here:

http://www.advancedaquarist.com/2005/7/aafeature

I personally have thought that if deeper sand gets flow to provide nutrients aided by infauna transport and channeling it can denitrify at least in the early years and perhaps do a bit more denitrification than a shallow bed with the same footprint since the deeper bed simply has more sand and surface area.

However, this study seems to suggest otherwise. At relatively high bioloads, nitrates were kept low equally well in 2.5 cm (1 inch) or 9cm(3.6 inch ) depths of sand. This suggests the extra sand depth doesn't help in tanks with live animals and infauna ;just as it didn't in the sterile tanks in the first experiment.
The live sand and rock where in the tanks for over 4 months( 128 days) and the animals for 118. Given 5 months ,6 months a year: Would deeper sand reduce more nitrate than shallower sand ? I have no idea but the study showed it didn't and that 1 inch beds kept nitrate low and depth didn't make a difference in tanks with infauna and other animals over a 128 day experiment time frame..

While the nitrate reduction with shallow and deep sand did not vary in this experiment ; it was interesting to me that the the tanks holding fish live rock ,live sand and invertebrates and fed pelletized food in this experiment reduced nitrate to lower levels than the relatively sterile tanks in the first experiment where only ammonium chloride was dosed .Bioload was pretty high and the folks doing the study seemed to be pretty rigorous about equating food inputs to the earlier ammonium chloride inputs.

Does anyone have a plausible explanation as to why the live tanks reduced more nitrate than the sterile ones ? I have a thought on it but would rather hear from others before tossing it out there.

 

[Scopus Tang]

I for one have never heard of a 6 square foot minimum ; don't know what it means in terms of tank size or sand volume or how it is relevant.

For those who wish to read it the second article/study, it is here:

http://www.advancedaquarist.com/2005/7/aafeature

I personally have thought that if deeper sand gets flow to provide nutrients aided by infauna transport and channeling it can denitrify at least in the early years and perhaps do a bit more denitrification than a shallow bed with the same footprint since the deeper bed simply has more sand and surface area.

However, this study seems to suggest otherwise. At relatively high bioloads, nitrates were kept low equally well in 2.5 cm (1 inch) or 9cm(3.6 inch ) depths of sand. This suggests the extra sand depth doesn't help in tanks with live animals and infauna ;just as it didn't in the sterile tanks in the first experiment.
The live sand and rock where in the tanks for over 4 months( 128 days) and the animals for 118. Given 5 months ,6 months a year: Would deeper sand reduce more nitrate than shallower sand ? I have no idea but the study showed it didn't and that 1 inch beds kept nitrate low and depth didn't make a difference in tanks with infauna and other animals over a 128 day experiment time frame..

While the nitrate reduction with shallow and deep sand did not vary in this experiment ; it was interesting to me that the the tanks holding fish live rock ,live sand and invertebrates and fed pelletized food in this experiment reduced nitrate to lower levels than the relatively sterile tanks in the first experiment where only ammonium chloride was dosed .Bioload was pretty high and the folks doing the study seemed to be pretty rigorous about equating food inputs to the earlier ammonium chloride inputs.

Does anyone have a plausible explanation as to why the live tanks reduced more nitrate than the sterile ones ? I have a thought on it but would rather hear from others before tossing it out there.

Tom where did you see 6 sq. feet as a minimum? I posted four to six inches as recommended depth for sandbed, but I didn't see the 6 sq. foot minimum post - perhaps I missed it.

As to your second question - did they? While the nitrogen in the first data began as ammonia - so we were able to track the total amount converted, the "food" in the second experiment isn't all going to convert to ammonia and therefore to nitrate. In fact, the second experiments states that the average ammonia levels in the tanks was always less than that of the tanks in the first experiment. If ammonia levels were less, it only stands to reason that nitrate levels are also going to be less.

From the article;
"Time series plot of the mean ammonia concentration (mg / L) in experimental aquaria. Note that the ammonia concentrations throughout the entire experiment are lower than those observed in the dosing experiments reported in Part 1"

 

[tmz]

Scopas,
The 6 square foot thing was in post# 500; not your post.. I have no idea what it means and clarification would help

Ok, I agree the two experiments really can't be read together since conditions varied significantly.
I think since live rock and live sand was used and foods and waste containing C,N and P fed the tank as well, it is possible that heterotrophic denitrifying bactertial activity was stronger in the second experiment ,since these bacteria need all three(C,N and P) ;not just the N from ammonia. The denitrifying bacteria in the first experiment may have been limited by a lack of C or P. But again can't really support that with these experiments since conditions varied as much as they did. Not a fault of the study since the effects of the different nutrient sourcing metjhods goes beyond the researcher's hypothesis, which is that sediment depth beyond and inch and grain size doesn't matter in nitrate reduction with or without live sand, live rock and live animals.

 

[longfellowship]

from the figure above nitrate stability only maintained to 0 in the later stages in the deeper sand bed with fine medium. This experiment wasn't long enough to see if these leveled off there or continued to go up, with nitrate production outpacing removal. Long term stability is the key question. Also keep in mind these tanks have a significant amount of LR for their size, which is not necessary in a DSB.

6 square feet is a rule of thumb given by Dr. Shimek where the DSB can support a larger array of infauna of various sizes. This contributes to long term stability. A smaller DSB can be run, but it is not as forgiving and will need to be more actively maintained with more frequent recharges and/or more disciplined predator exclusion.

JD

 

[longfellowship]

from the figure above nitrate stability only maintained to 0 in the later stages in the deeper sand bed with fine medium. This experiment wasn't long enough to see if these leveled off there or continued to go up, with nitrate production outpacing removal. Long term stability is the key question. Also keep in mind these tanks have a significant amount of LR for their size, which is not necessary in a DSB.

6 square feet is a rule of thumb given by Dr. Shimek where the DSB can support a larger array of infauna of various sizes. This contributes to long term stability. A smaller DSB can be run, but it is not as forgiving and will need to be more actively maintained with more frequent recharges and/or more disciplined predator exclusion.

JD

The more I look at this figure, the more I wonder where any conclusions that sand bed depth and substrate size don't matter came from. Even without the long term problems of cementation without adequate fauna you can see an obvious separation between the deep fine and the rest. The author's conclusions were focused on the difference between plenum and non-plenum so this conclusion must have been taken out of context and perpetuated here. It is a very good lesson on why looking at data carefully and not forming long term opinions on a statement or experience taken out of context is very important.

JD

 

[tmz]

The author's conclusions were focused on the difference between plenum and non-plenum so this conclusion must have been taken out of context and perpetuated here.

Not out of context: the researchers offered more than conclusions on plenums in both studies as noted below.
Stating information is presented out of context when it clearly is not is convenient to your position and implies anyone who questions that position must be misinformed, incapable of understanding it or lacks intellectual integrity .Not really a good start to a learning discussion.

From the second study(http://www.advancedaquarist.com/2005/7/aafeature):

Each sediment-based aquarium design appeared capable of handling nutrient inputs up to 0.5 mg / L / day of NH4+ - which is equivalent to a well-stocked reef aquarium. At this input level, final concentrations of ammonia, nitrite and nitrate did not differ significantly among aquaria 1) with or without plenums, 2) containing deep (9.0 cm) or shallow (2.5cm) sediments, or 3) containing coarse (2.0mm) or fine (0.2mm) mean particle sizes. Bioload and animal deaths in the aquarium show a much greater effect on the water quality than does the specific design for the tank.

and

Overall, both the results of the dosing and live animal experiments suggest that there is no measurable difference between most of these common sediment filtration designs for maintaining suitable water parameters. There were no significant differences among depth, particle size or plenum treatments for the processing of ammonia or nitrite in recirculating aquarium systems. Deep, fine sediments had the lowest average final concentration of nitrate in these trials, but these values were not significantly less than the average final concentration of nitrate in shallow, coarse sediment treatments. Also, contrary to our expectations, the presence or absence of live animals and sandbed infauna made no significant difference to the nutrient concentrations across the time periods tested here. So what does explain the differences among aquaria in these experiments? Well, it turns out that the best predictor of aquarium nutrient levels is quite simply the bioload and any animal deaths in the tanks



and from the first study(http://www.advancedaquarist.com/2005/6/aafeature):

In terms of processing nitrogenous wastes from aquarium inhabitants (specifically ammonia, nitrite and nitrate), none of the experimental treatments (plenum vs. sandbed; deep vs shallow; coarse vs. fine) appeared to have a significant advantage (Figs. 7-9). After an initial

and

# We show that even among identical tanks set up in a laboratory without any live animals, there can be dramatic differences in performance from one aquarium to the next (see Figures 2 & 3 above). Our results highlight the problem with any study lacking proper replication, and in which there are no controls. We argue that anecdotal evidence is simply presentation of an opinion in cases such as this, and more than 5 years of heated debate has resulted from the staunch defense of these opinions.

# We urge hobbyists to develop a good 'BS' detector that will allow you to question information presented to you without any experimental evidence to support it.

 

[tmz]

The links for each of the studies are reposted in the post above for those who would like to read them and draw your own insights and conclusions as to the findings.

 

[longfellowship]

Not out of context: the researchers offered more than conclusions on plenums in both studies as noted below.
Stating information is presented out of context when it clearly is not is convenient to your position and implies anyone who questions that position must be misinformed, incapable of understanding it or lacks intellectual integrity .Not really a good start to a learning discussion.
[/B]

A fair criticism and perhaps overstated on my part. I should have reviewed the authors statements rather than go from memory in my haste. Appologies. What I was really getting at is that the experiment was primarily designed to see if there was a difference in plenum versus non-plenum. The substrate and depth variables were put in to cover their bases. Regardless I strongly disagree that the differences were insignificant based on their own data set. The fact that the deeper SB hovererd at 0 after 80 days while the others started to rebound points to a system in equilibrium versus others that are obviously not. The study was cut off, while the nitrate was on the rise for all but the deep fine.

JD

 

[tmz]

Maybe the nitrate reduction would have tracked better in deep fine sand as time went on; maybe not. But it was their interpretation that the nitrate variations in firgure 5 were insignificant with a vague attribution for variations to bioload and animal death;not a perfect explanation for sure. However, they did use a statistical analysis to weigh the variables. It's been far too long since I studied statistics for me to pretend I can make any sense of that section other than that they seem to have included the right variables.
I agree this study like all others should be critically read along with the data
It does ,however, offer a 4 month comparison with multiple sets of conditions.Both of their studies clearly show that nitrate reduction occurs in shallow sediment.
The main issue that bothers me about the writings on DSBs is the dearth of a discussion about the denitrifying microbes(facultative heterotrophic bacteria) ostensibly supported in them ,the needs of these organisms for N,C anP and adequate water movement into the bed to provide it.Most discussions on remote deep sand beds (in a bucket for example) discount the dynamics of diffusion, advection and live infuana completely. Deep live beds in lighted tanks with reef like rock obstructions seem a better bet to me. Overall, deeper is not necessarily better for nitrate reduction, in my opinion and deeper beds pose some increased risks for anoxia and hydrogen sufide issues. Will infauna help insure nutrient availability deep in the bed and support the hypoxic conditions needed for anaerobic activity? Perhaps if it's healthy enough for long enough. Keeping it so ,may not be easy. On the other hand will shallow sand and bacterial mats provide hypxoc environments ? Yes , I believe so.

 

[Paul B]

If I am reading this correctly (and I probably am not) they did these tests for 80 days.
If that is correct, it means absolutely nothing.

 

[longfellowship]

If I am reading this correctly (and I probably am not) they did these tests for 80 days.
If that is correct, it means absolutely nothing.

Paul,

You are not too far off. It went to 118 days.

I think we should all pool our resources and fund a 7 year study. Since you are the "expert" and have a track record of keeping a tank long term and not screwing things up or getting bored and doing a cannon ball into your tank, I vote we do it at your place. Of course to do it right we will have to set up about 12 different 100 gallon tanks, all with exaclty the same livestock and the same brand of beer can. Then you'll just have to take weekly readings on all the tanks for seven years and document it here. Sounds like fun. Kind of makes you wonder why this has never been done before. :idea:

 

[Paul B]

It works for me. It will take me a few years to collect another 11 Budweiser beer cans though. Most of the cans in the Sound are Coors, I am not sure they would work.

But if those tests went to 118 days, the information is useless. The thing is barely cycled in that time and most of the bacteria that will finally settle down in there, have not even arrived yet.
You are correct, you need 12 tanks exactly the same for 7 years, I would go 20 but I probably will not live that long.
Nothing happens in a tank in 118 days (I have amphipods older than that) so they wasted a lot of time and money. :dance:

 

[rivoth]

Longfellowship,

The logistics of a long term study with large tanks and sufficient controls and redundancy make such a study highly unlikely as you hinted. Plus we might not even agree on what the study goals should be.

I want a sandbed for the additional diversity of life it generates, Even if I could maintain a higher coral and fish bioload with a bare bottom design I wouldn't go that route. I am interested in what sand bed design choices like depth, sand size, surface area, display vs refugium, and stocking choices will provide: high animal diversity, and a greater capacity to process heavier feeding for my corals with minimal artificial filtering. It would also take a whole lot of proof to convince me that I should clean or replace sand beyond that which dissolves.

The people who are probably in the best position to advance the knowledge base are those in the aquaculture business. High growth rates with low maintenance costs help their bottom line. Unfortunately, competitive pressures tend to keep their data from being openly shared. Most scientists don't have much interest in improving aquarium system knowledge since they are artificial environments. Certainly vendors of expensive skimmers aren't interested in alternatives. Hobbyists are well meaning, but not really in a position to do more than guess why their systems work or fail.

So for now I try to model my system after one of Eric Borneman's tanks that I admire. The last 2 1/2 years have been a great learning experience and I expect it to hold my interest for many more to come.

 

[tmz]

Thanks to all for a spirited and informational discussion.

I think Paul would like to run the experiment for another 40 yrs but it would be hard to replicate as he has some unique materials in his system. Anyway I don't think Paul could be persuaded to install a deep sand bed.

Not to quibble but they used a 128 day time frame . 10 days without animals on the front end as I read it. Not sure why more time beyond 4 months would make a difference but it might.

I think in display deep sand beds ( several inches or more) are a nice way to set up an aquarium for the diversity they offer . Whether they are superior in denitrification to other methods has been debated for years and likely will be for years to come and in large measure depends on the conditions in the bed and the specific aquarium.
Knowing that significant denitrification occurs in shallow depths opens up other options.
How long deep sand beds can function without spewing toxins and nutrients as well as the best ways to maintain them are still open questions too,imo.
Other approaches are also nice ways to set up an aquarium and a good bit of diversity can be a achieved in shallow beds, live rock, chaetomorpha refugia, cryptic zones,etc.,ime.

I hope whatever method is chosen that the hobby experience enhances your life experiences and perspectives and results in reef tanks that please you as individulals.

 

[rivoth]

How long deep sand beds can function without spewing toxins and nutrients as well as the best ways to maintain them are still open questions too,imo.

What would be the biological or chemical mechanisms that would cause a deep sand bed to switch to spewing toxins and nutrients?

 

[tmz]

Clogged areas , no water exchange, anoxia ,sulfate reduction with sulfides and hydrogen sulfide , localized ph drops and breakdown of refractory organics holding metals and increased TOC are a few that I'm concerned about, in older beds.

 

[Scopus Tang]

It works for me. It will take me a few years to collect another 11 Budweiser beer cans though. Most of the cans in the Sound are Coors, I am not sure they would work.

But if those tests went to 118 days, the information is useless. The thing is barely cycled in that time and most of the bacteria that will finally settle down in there, have not even arrived yet.
You are correct, you need 12 tanks exactly the same for 7 years, I would go 20 but I probably will not live that long.
Nothing happens in a tank in 118 days (I have amphipods older than that) so they wasted a lot of time and money. :dance:

Dang! Wish I would have know that we were going to need those - cleaned out my Grandfathers shop a couple years ago when he passed away and threw a number of them out.

While I agree that the shortness of the study doesn't do anything for supporting their conclusions long term. I don't think we can necessarily throw the baby out with the bathwater. Regardless of other errors, as Tom stated, the studies both clearly show that nitrate reduction does occur in shallow sediment; at least for a short time period. That to me is interesting simply because everything I've read previously says that the shallow sandbed is not capable of nitrate reduction.

 

[Paul B]

QUOTE]I think Paul would like to run the experiment for another 40 yrs but it would be hard to replicate as he has some unique materials in his system. [/QUOTE]

Great but I will most likely be very dead by then, or very senile. More than I am now.

Anyway I don't think Paul could be persuaded to install a deep sand bed.

I would rather stick a bristleworm in my eye.

Dang! Wish I would have know that we were going to need those - cleaned out my Grandfathers shop a couple years ago when he passed away and threw a number of them out.

Your Grandfather's beer cans are no good, you have to collect them in the sea to be considered "natural" otherwise they are called "Garbage" Big difference.

Regardless of other errors, as Tom stated, the studies both clearly show that nitrate reduction does occur in shallow sediment; at least for a short time period.

I don't think so. much too short to show anything except that some scientists could keep a tank going for 118 days. :rolleye1:

 

[Scopus Tang]

Your Grandfather's beer cans are no good, you have to collect them in the sea to be considered "natural" otherwise they are called "Garbage" Big difference.

Alright, its good that I didn't keep them then. I'm sure I could find you some "natural" ones from up in the Big Horns, but they would be full of bullet holes ):, so still may not be what you are looking for.

 

[rivoth]

Clogged areas , no water exchange, anoxia ,sulfate reduction with sulfides and hydrogen sulfide , localized ph drops and breakdown of refractory organics holding metals and increased TOC are a few that I'm concerned about, in older beds.

Those might be concerns, but they really need some fleshing out to be called mechanisms.

For instance hydrogen sulfide breaks down very quickly when it reaches oxygenated areas, so unless you go digging deep in your sand bed it won't be an issue. It also is extremely odiferous so you'll know right away if it is getting released. If you can't smell it, there is not enough of it being released to harm anything. Given continued presence of sand worms it would have no greater concentration in an old tank than a 2 year old tank.

Dissolved organic compounds (plus dissolved metals) can be kept in a steady state with Granulated Activated Carbon, export through refugium algae growth, algae turf scrubbers, some types of coral growth like xenia and water changes.

Particulate organic compounds will reach a steady state through filter feeders, settling out to the sand bed to be eaten by infauna and bacterial breakdown. Lacking predation and given proper living conditions, sand bed fauna will grow in population to match the food sources. This will result in a steady state being reached where food breakdown rates match food addition rates. So non inert organic sources in an 10 year old sand bed should be about the same as in a 5 year old sand bed. Inert materials are just another form of silt/sand.

You need to define clogging. If you are talking sand cementing, the only mechanism for that to happen is if there very large PH swings. That indeed would be a problem, but a drop in PH requires a maintenance failure. The sand bed can not do that by itself. Maintenance failures will cause a tank of any design to have serious problems.

Water exchange within the sand bed is on going with the presence of sand burrowing worms and crustaceans. Even though Paul doesn't think he'd want to burrow 6 inches under the sand, my worms have no problem with it, as evidenced by the worm tunnels against my glass that go all the way to the bottom of my 6" sand bed.

I don't know about you, but I'm anal about setting up a very good water flow system in my tank. There are no dead spots so regardless of what mechanism you have in mind for localized ph drops, they would never be able to drop to a harmful level. If you are talking about dead spots within many reefers walls of rocks, that's a function of the rock work, not the sand bed.

In the end I think crashes blamed on sand beds boil down to the likely hood of making a serious husbandry mistake as a function of time. If I'm mistaken about that then there should be a clearly defined mechanism for failure that is specific to an older sand bed. I really don't see one.