Lower reduction rates of NO3 from the DBS, evidence of a carbon limited system

[Plantbrain]

Carbon limited denitrifyers, or why my DBS doesn't remove NO3 ?

I've noticed a number of reef folks keeping such low nutrient lebvels in effort to stop noxious algae have had trouble with their DBS's and plenums' rates of NO3=> N2 reduction.

I looked into why they had trouble and why they had issues with start up, the reason was rather simple but not obvious to many.

The denitrifying bacteria were carbon limited. Not CO2/HCO3, CO3 limited, but organic carbon, you know, the stuff we eat for food Plants/algae/some bacteria use the DIC, the rest of us use the organic sources.

If you look at the batch denitrifiers and other devices that use bacteria to reduce the NO3, you'll see they also have special foods they sell, generally Sulfur and alcohol(a source of carbon for the bacteria).

They do not need a lot, but they do need some.
Some foods are low in Carbon and the C:N ratio when trying to keep the nutrient levels very low ceertainly will play a larger role. As this ratio becomes more unbalanced, the NO3 builds up.
Flow resistrictions do occur even with critters in the the substrate over time. This can reduce bacterial populations as well.

I recently set up a new tank, I add vacuumed detrital mulm from an established flithy DBS. I've also used mud and peat as a source of organic matter, Miracle mud is essentially OM(Organic matter) with a few things like iron and CaCO3.
I do not use much, you don't need much to start off with, but you do need some, otherwise the bacteria have nothing to live and feed off of.

After a few months, the tank settles in and the normal cycling takes place from fish/critter waste/feeding.

I think folks have troubles when they try and go too clean and remove everything, then this cycling gets messed up and the bacteria starve and their populations go way down.

We have seen plenty of evidence for this in nutrient limited regions with low Carbon. Denitrification in wetland soils is well studied, the roles the nutrients play in this process are well studied as well. The ratios can play mportant roles.

The amount of these Ratios provided in the foods are critical since these amounts are often very limiting, this they will limit the denitrifiers which respond quickly to nutrient changes.

the OM added will provide a better environment initially(electron donors) for these bacteria which do well at a lower Redox, about 200-300mv, not a particularly high electron pressure.

See
White and Reddy 2000
White and Reddy 1999
Reddy and Patrick 1984


Regulators of this process:
Low O2, low Eh(200-300mv)
Presence of Electron acceptors NO3 etc
Electron donor sources: Organic carbon compounds, reduced sulfur compounds(Gee, go figure.... the same food they add to those denitrifying reactor tubes)
Temp
NO3 diffusion/flux to anoxic zones

This might help a few folks that have had trouble getting their DBS's going try some approaches to improve their balances.

Food and the C/N ratio might be a simple solution.

Regards,
Tom Barr

 

[sjvl51]

Makes sense.

Anthony Calfo recommends that we keep a nitrate level of about 0.2 since corals need nitrate as food. To get my nitrates to 0.2, I increased the amount of food. It worked for a while and then the tank adjusted (I assume bacteria increased) and the nitrates fell to 0 so I had to increase the food again. This supports your theory of food/carbon being a limiting factor.

Vickie

 

[Plantbrain]

I've been using KNO3 to supplement the NO3 rather than a bioload.

Then I can measure this and control this variable over a wide range without dealing with algae etc.

I namely deal with macro algae and their levels or uptake and wanted to know how much NO3 is removed by the bacteria versus the macro algae.

We deal with Caulerpa taxifolia weed issues at work/the lab and we might add a tracer of NO3 to see what fraction of NO3 is used by each group.

I'd say a lot more will be used by the macro algae and their good growth supresses noxious reef algae, while allowing more nutrients to be available to the coral. At least that is what I've found thus far.

The macro algae often used in refugiums supply the bacteria with carbon, through leeching, and also contribute to removal of NO3/PO4 etc, not just NO3 like the bacteria.

The issue arises, the macro algae need higher levels of NO3 than the bacteria for good growth. Dropping them very low and without a steady supply at low levels, causes the algae to perform poorly, perhaps even causing more issues than they help.

If a steady stable level of NO3 removal is achieved though....then nioxious algae issues are not a problem and good coral health is also acheived at higher nutrient levels.

So maintaining a stable well tended refugium will go a logn way to keeping the levels stabl;e and allowing the bacteria and the macro algae to do their job well. Adding food consistently also will allow a stable input of nutrients as well.

In a nut shell, it's a simple two box model, what goes in, must come out. If we want that to be stable and effective, then good pruning of the macro biomass will help or good export from the skimmers.

I'm curious as to how much organic carbon is removed by skimmers as well.

Regards,
Tom Barr

 

[sjvl51]

There have been at least one analysis on skimmate that I remember - possibly done by Dr. Ron. I'll see if I can dig it up. I think it was an article about exporting nutrients.

Vickie

 

[CaptiveReef]

NO3 Reduction

NO3 Reduction

Yes I agree with what you have posted, you have to maintain a bioload to keep a DSB in check. I use a wetdry in my system along with a DSB in my sump to maintain a low constant level to Nitrate to feed the symbiotic algae in the corals and clams.
You shouldn't strive to make the tank a sterile environment, you can create the same conditions with the right setup, low levels not saturation is the goal you look for with an enclosed system.
This is a great thread!!!!!!!

CaptiveReef

 

[Plantbrain]

Thanks Vicki, that would be great if you find anything on that, I could, but I'm obsessed with too many things at the moment and my boss(well, sort of a "boss") actually expects me to do some real work

We have some equipemtn at the lab, the elemental anaylsis can be done I think here locally at our lab. I'm not certain about other nutrients, but Cu, N, P, Ca, Carbon we can do.

I'm not big on skimming personally, I've always held that healthy plants = healthy critters. I have not used any meds in over 15 years using this idealology nor needed too.

Any interesting by product of good macro or plant growth, both in FW and SW systems: the lowering of NH4 to beyond detectable levels. The NH4/NH3 is used up before we can measure it.

Without the macro's hungry uptake of the trace amounts of NH4, the algal spores have a nice rich meal of NH3/NH4, which has 8 electrons less energy requirement for assimilation into glutamine.
This does not mean that much to a large macro alga, but to a tiny small algal or Cyano spore, this is payday.

If it was an organic nutrient bound issue, the macro algae refugium method would not supress the noxious algae.
Also, activated carbon/resins would prevent organic bound N and P from building up and causing algae blooms. Water changes would have a greater effect as well.

PO4 is somewhat of an enigma in the SW system, we can add it liberally, 2ppm is not uncommon in a planted FW tank, no algae and intense plant production rates, O2 evolution that makes the tank look like a champagne. I always get a diatom blooms with dosing it at higher levels. I believe the range is much lower with SW systems but a good set of results might be obtained with more careful useage.

Don't add PO4 to a Reef tank, let me work with the macros and see how they respond, they grow back fast and have high uptake rates. Eventually I'll uncover some of the issues the poor folks have with noxious algae and then you guys can focus much more on the health and nutritional needs of the Corals and other critters.

That's the goal, good coral and critter health for most folks.
When they do well, the noxious generally do not. We see this pattern throughout nature. I did this in lakes, ponds, FW planted tanks, I think some of the same things apply here as well. But we must be careful not to jump from the pond to the sea

Still, the destruction and toture of macros is good, we need to know how to induce the noxious algae critically and do it repeatedly. Then go back and test it. Not many folks are willing to do this with their reef and SPS tanks This process allows a much greater understanding of what really causes algae issues than non controlled tank treatments.

Regards,
Tom Barr

 

[sjvl51]

Tom, here it is - http://reefkeeping.com/issues/2002-12/rs/feature/index.htm

Vickie

 

[sjvl51]

Re: NO3 Reduction

Re: NO3 Reduction

Yes I agree with what you have posted, you have to maintain a bioload to keep a DSB in check. I use a wetdry in my system along with a DSB in my sump to maintain a low constant level to Nitrate to feed the symbiotic algae in the corals and clams.
You shouldn't strive to make the tank a sterile environment, you can create the same conditions with the right setup, low levels not saturation is the goal you look for with an enclosed system.
This is a great thread!!!!!!!

CaptiveReef

I agree that too many people are making this hobby too difficult. A low level of nutrients/a few pieces of algae, to me, is more natural than a hospital clean tank. I would just as soon relax instead of worrying and investing a lot of effort to remove the last bit of algae so that I can feed my critters algae (otherwise known as nori, etc). I wouldn't want my tank to be overgrown with algae either.

Vickie

 

[Plantbrain]

Yes, even the bacteria in the live rock can become carbon limited through excessive stripping.
What's good for the macros, is often good for the bacteria and corals. Less is not better, although many folks often imply this.
Some of the data is misleading, but he addressed some of that as far as the Caulpera/Xenia.
The metal increases are very classic though.............many fo the trace mixes are designhed for hydroponics and terrestrial plants, not reefs or macro algae. Trace specific _ratios_ can easily improve the issues Ron brings up. Eg , reducing the copper levels and others.

But , with only an N of 3 or 4, this is hardly a slice of data to trust fully. Many variables go into each person's tank there. I'm very leary of that. Still, it gives some rough idea what we might expect.

Given copper's toxicity to a wide range of animals yet essential to photosynthetic animals/plants/bacteria, it might wise to use a Cu free trace and then monitor and dose Cu seperately.

But then that is not so easy either............which is what folks are trying to acheive.

Nothing like a good old 50-70% water change to remove all the testing and work. Takes a lot of the guess work out of things. Cost a bit to do it often though but would remove any build up.

This method is extremely easy and useful in FW systems and dosing, but the salt mixing and cost for water changes might not be such a bad deal given the cost and operating expense of other devices........

Regards,
Tom Barr

 

[sjvl51]

Tom, if you consider the cost of all the additives that many people add to their tank, doing frequent water changes is not that expensive IF you stopped the additives as well.

I do a 25 gallon water change (on about 200 gallon system) twice a month. A 200 gallon pail of IO costs (here anyway) about $70 Cdn. This means that one pail will last about 4 months and cost me about $18 per month. That is not a large amount when you consider the cost of various additives. I add iron (for the macro algae), CaCl2, baking soda and magnesium (as test results show a need). The only other additives is Salifert Amino Acids and kalkwater. I estimate it costs me about $25 per month when I factor in Phosban and carbon as well. I change the carbon with each water change and Phosban when the PO4 starts to rise.

JMO

Vickie

I should add that I realize one 50 gallon water change is more effective. I just have to figure out where I can put the second Brute container.

 

[Plantbrain]

If you do a cost anaylsis on a 25 or 50 gallon reef, macro tank etc, then a weekly 50% water change is not much.

Add the cost of a good set of test kits etc as well.
I do not like IO, I use the RedSea, I get a 200 gal tub for about 45$ USD, but I have connections and business deals. 55-70$ is more common.

Larger water changes do great things for reef tanks, especially if you are at a loss for solving the problem or don't have the time to solve it before your SPS frags all die.

It removes many unknown variables and re sets the tank like making a standard reference solution.

Many folks have gotten very techy and away from some very basic methods that work.

All we used in the distant past was IO, water changes and a UG filter. We did not even have submersed powerheads back then.

The tech stuff is fun, great, impresses the friends, is useful for larger systems, where cost of the water changes and the associated hassle there makes life tougher and more costly, but I think many simply forget the basic idea...........and assume they have to have all these goodies.

From a beginner's approach, doing the water changes is easier in most cases.

No testing, dosing, removes the unknowns, exports everything, maintains good levels, removes any allelopathic chemicals (so does carbon), livestock loves the new water etc.

But a well run refugium is very low maintenance also
Better the seaweeds than me!

Regards,
Tom Barr

 

[sjvl51]

To be honest, Tom, my 25 gallon refuge was full of racemosa that I had to harvest every couple of weeks. Then I thought that I would add some other macroalgae (a few mangroves, chaeto, couple of caulerpas, etc). Within a couple of weeks my racemosa disappeared (it just didn't grow any more) and I thought I had plenty of nutrients before.

Now I have a couple of small handfuls of chaeto in my grow out tank, half of my mangroves left (about 7), and a very small clump of caulpera in the refuge (about 5 leaves). I think my racemosa has completely died.

I increased the lighting over the refuge which didn't help. I dose iron on a weekly basis and magnesium when below 1300. I still can't get the macroalgae to grow. Something is limiting the growth but I can't figure out what. I do get cyano on the sand (sometimes more than others) since adding the new sump and the 60 gallon display tank. I had this problem before I added the phosphate reactor. PO4 runs 0.03 and NO3 runs 0.2. I moved the chaeto and mangroves to the sump in case there was chemical warfare going on.

If you see something that I'm missing, please let me know. I find this frustrating with only 5 leaves in the refuge. I know I had more pods when the refuge was full of racemosa.

Vickie

 

[Plantbrain]

Simple, add KNO3. About 1/8 teaspoon will do it.
That will add about 5ppm of NO3.
You can dilute this into DI water and dose more accurate measures should you chose to do so.
KNO3= stump remove, you can get it at Home depot.

If you have good Ca and KH, and dosing the traces, this is all that's left, macro's do well without much PO4.

NO3 on the other hand will limit them.

Also, NO3 test kits, any test kit for that matter are inaccruate at low levels. I use a hanna colorimeter with multiparameters........but not many folks use this
These are extremely accurate to 0.1ppm of NO3 and 0.001 NH4.
There is some error within this even, but it's far better than any test kit used by a hobbyists.

Lamotte kits are decent.
I do not trust others.

also, cyano=> NO3 limited system.
They do well at low NO3 inorganic levels.

I'd remove the PO4 remover, the algae will remove that just fine, you are likely telling the algae that it's going to be very lean and they respond by dying back and sporulating("seeds" to make through till conditions are good again)

At such low nutrients levels, SRP and N test kits are often off.

I calibrate my equipment with known standards, you can do this as well.
KH2PO4
KNO3
Trace mix

Dilute into know volumes of water, eg 1 liter of DI water.

1 mg/l = 1 ppm etc.

The indicator plants/algae/cyanos tell me more about your tank than the test kits ever will

There are two ways to beat cyanos before you correct the NO3 levels: black for 3 days or erythromyacin(antibiotic). I think the "Redslime remover" is EM.

I'm not big on either of these for SW, I pick and clean off, do a water change, then add NO3 back. You can also feed the fish a bit more also to add more N.

Regards,
Tom Barr

 

[sjvl51]

Like you, I don't like to use chemicals. They usually end up causing more problems in the long term.

I figured the cyano was caused by the new tanks added to the system (new sand and maybe 10% more dead rock) With the spreading out of the living rock from 1 tank to 3 tanks, everything was upset. Before that I had very little cyano so I was blaming it on new tank cycle. I'm one to believe that a new tank must go through various stages and I don't get to upset about cyano. Like you say, if there is too much, I clean it out and then let the tank do its job.

I did loose some circulation with all the changes. We are waiting for pumps to come in to hook up the 2 closed loops. I'm sure when the dead spots near the sand are taken care of, I'll have less cyano.

I'll look in Home Depot for KN03. Again, that sounds like a chemical which I try to avoid.

What I have started to do (for various reasons) is feed more phyto. This always adds some extra nutrients to the system as I like to feed as the phyto goes into the stationary phase or at the end of the exponential growth. Not all the nutrients are used up so some get added to the tank. I have noticed since I started doing that, that the caulerpa in the refuge went from 3 leaves to 5 leaves.

Since I was getting a NO3 reading, I didn't realize that was limiting the growth. I'll monitor the NO3 and see if I can increase it to closer to 1.0.

I think I'll leave the Phosban in the system. As it gradually stops becoming effective, the PO4 should gradually increase allowing the macroalgae to take over. Corals, etc don't like sudden changes. As long as the PO4 stays low, I won't change the media (again, I'm not aiming for 0 phosphates, just low phosphates). I may not get great SPS colours but I'll see how it goes.

Thanks for pointing me in the right direction. I now know what to monitor and adjust as necessary.

Vickie

 

[Plantbrain]

KNO3 is not a "chemical herbicide/anitobiotic", it's a fertilizer and a salt. You add fish food, you eat food, those are chemicals as well. It's not anything to worry much over, think of it as macro algae food.
If you add new rock, some of the bacteria and other critters die off, that decay turns to NH4, lowers O2 levels and feeds smaller noxious algae.

The macros need NO3/NH4 to grow. NH4 often is not supplied at high enough levels to support the N growth needs/demands.
You can add fish food which needs to be broken down to NH3/NH4 to NO2 and then to NO3, or you can cutr to the chase and add NO3, which smaller noxious have a more difficult time utilizing than the larger macros.

The other big issue using NH4 waste, it's pH dependent and NH3 is a much larger ratio at higher pH's above 7. So any present in a pH 8.2-8.3 range will be the much more toxic form of NH3, while soft water FW systems with a pH of 6.0-6.5 have namely the NH4 form.

Here's a listing of it:

This is a good example of
chemical equilibrium at work:

As the unionized ammonia (NH3) is removed -- by ANY action -- the equilibrium will shift and more unionized NH3 will be produced, to keep the ratio ammonium:ammonia (NH4+:NH3) constant.

So, as the NH3 is being continually removed, all ammonium will be
converted to ammonia -- and removed!

One thing of practical importance that we don't know is how FAST the ammonia will be removed, thus how fast the water will be detoxified.

Ammonium and ammonia have an equilibrium relationship that varies with pH and temperature. The percentage in the dissolved but not ionized ammonia (NH3) form, at 20C, jumps from 0.5% at pH=7 to 13.7% at pH=8.5. [Spotte,
> 1970, p104] That means that 86.3% remained as the ion (NH4+) form, so that *most* is still harmless ammonium.

However, the basic *toxic* material is over 27 times higher at a pH of 8.5, until we do something to remove it, such as long-term aeration, biofiltering, plant feeding, etc. In any compromise between food and poison, the poison will inevitably win.
The overall toxicity of ammonia can be altered by lots of other factors. Supersaturation with oxygen seems to reduce damage, somewhat. Nevertheless, ammonia is lethal at levels well below what the average test kit can indicate, and the stunting and subtle disease-inducing damage can be severe at far, far lower levels.

Spotte goes on to point out that Burrows (1964) found clubbing (hyperplasia) and permanent damage to gill filaments of salmon fingerlings at levels of ammonia of 0.006-0.008 ppm (0.3 ppm total ammonium/ammonia). [This was at a pH of only 7.8, BTW.] The younger fish never recovered, when returned to clean water. They were stunted, permanently. Older fish did recover after 3
weeks in new water. Results on minnows and other fish were much the same, so the damage was deemed to not be species specific. Burrows suggested that exposure to ammonia at such levels also was the precursor of bacterial gill diseases.

This is with fish, perhaps a similar issue exist with corals and inverts, I have no idea. But NH4 is playing with fire, NO3 is much more benign and useful as far as a NO3 source.

Sometimes we add too little N from fish waste food etc, sometimjes too much. By topping it off a little, it can help.
I did not find any patterns in the macro algae tanks at 5-10ppm of NO3. The PO4 was very low, adding KNO3 drives the PO4 uptake of the macro algae and limits PO4.

If you add everything else in excess, the PO4 will be driven down and maintained as limiting nutrient.

The same is true for NH4, adding another source of N allows the plants and corals to make the enzymes needed to get the NH4 in the first place without giving the smaller noxious a chance at this free "NH4 candy". There are 8 free electrons in NH4 vs NO3, making it one of the most energetic chemical reactions in biology tio reduce NO3 to NH4 and on to glutamine.

This is a method to rid yourself of using the PO4 ban, you limited the NO3, not the PO4, so the PO4 builds up, it's in excess relative to N.

Adding Phyto will help and produce more N, NH4.
Nothing wrong with that up to a point.

There is a point where adding more critters/fish etc adds too much NH4 abnd that's why you cannot add more and more, it's not due to the PO4 directly.
NH4 is dang nasty as well.


You folks just cannot measure it easily since it's used up before you can measure it(Bacteria-new rocks not yet established, macros, noxious algae, corals, Xenia etc), except at very high levels.

We can dope the N15 and use that to trace where the NH4 is going. That and good measurements and tissue anaylsis can answer the main question.

I hope to do this with FW and SW systems in the coming months/year.

Regards,
Tom Barr

 

[sjvl51]

Tom, bear with me. High school chemistry was a very long time ago and it takes a while to wrap my mind around what you are saying.

We have found with baking soda/washing soda, there in Canada, some brands have perfumes/surface enhancers added that are not listed in the ingredients (compared to same brand name in the US).

Because of the different regulations, KNO3 may not have the same composition as your KNO3 and may not even be available. I didn't have enough time when I was in town today to search for this, but I hope to tomorrow. This is one reason why I am very careful to confirm what I am doing.

KNO3 is not a "chemical herbicide/anitobiotic", it's a fertilizer and a salt. You add fish food, you eat food, those are chemicals as well. It's not anything to worry much over, think of it as macro algae food.
If you add new rock, some of the bacteria and other critters die off, that decay turns to NH4, lowers O2 levels and feeds smaller noxious algae.

Adding more food is not a problem as long as I am assured that it wasn't changed to meet Canadian standards. ie We can't buy pickling lime (used by many for kalkwater) here in grocery stores. I believe some have found it, in bulk, at chemical supply places.

The macros need NO3/NH4 to grow. NH4 often is not supplied at high enough levels to support the N growth needs/demands.
You can add fish food which needs to be broken down to NH3/NH4 to NO2 and then to NO3, or you can cutr to the chase and add NO3, which smaller noxious have a more difficult time utilizing than the larger macros.

I can see the logic behind just adding what you need without "extras" that the tank has to process/remove. It would just take time to fine tune the amount needed.

This is with fish, perhaps a similar issue exist with corals and inverts, I have no idea. But NH4 is playing with fire, NO3 is much more benign and useful as far as a NO3 source.

I agree, NH4 does not sound like something I would want to high in my tank for the fish and I assume the snails, crabs, etc would be affected as well.

Sometimes we add too little N from fish waste food etc, sometimjes too much. By topping it off a little, it can help.
I did not find any patterns in the macro algae tanks at 5-10ppm of NO3. The PO4 was very low, adding KNO3 drives the PO4 uptake of the macro algae and limits PO4.

If you add everything else in excess, the PO4 will be driven down and maintained as limiting nutrient.

The object, if I understand correctly, is to remove NO3 as the limiting factor and make PO4 the limiting factor. In that way the macroalgae would continue to grow until they ran out of PO4 which would reduce the PO4 from 0.03 (at present) to something less - maybe undetectable by the test kit.

Sounds like a good way to go.

The same is true for NH4, adding another source of N allows the plants and corals to make the enzymes needed to get the NH4 in the first place without giving the smaller noxious a chance at this free "NH4 candy". There are 8 free electrons in NH4 vs NO3, making it one of the most energetic chemical reactions in biology tio reduce NO3 to NH4 and on to glutamine.

NH4 is ammonia, right? I thought ammonia became NO2 (via bacterial action) which then became NO3 which had to be exported via water changes or broken down in the sand bed. How do you "reduce NO3 to NH4"? Glutamine is food for plants or ?? Is this reaction taking place in the plants as opposed to the nitrogen cycle which takes place in the water? Is that where I'm mixed up?

Adding Phyto will help and produce more N, NH4.
Nothing wrong with that up to a point.

The phyto would add more N, NH4 but I was more concerned with the f/2 fertilizer that I use. By adding the phyto as the growth slows down, all the fertilizer is probably not completely used up so I would be adding f/2 fertilizer as well. I'm not sure what the limiting factor in the f/2 fertilizer is. It could be NO3 or PO4. I would assume which would mean that I could be adding excess PO4 instead of NO3 which would make matters worse not better.

The fact that I have seen an increase in macroalgae growth (since increasing my phyto added to the tank) tells me that I am adding some of the limiting factor (for macro algae growth). I'm just not sure what.

There is a point where adding more critters/fish etc adds too much NH4 abnd that's why you cannot add more and more, it's not due to the PO4 directly.
NH4 is dang nasty as well.

Our glass cages have many limitations. I am very conscious that the electric line ends at our house. In other words, whatever happens to this section, our electricity is affected. With this in mind, I plan on keeping to a lightly stocked tank so that the losses due to oxygen levels will be minimal. This does limit the amount of fish/critters I add to the tank but I had never thought that adding more livestock would reduce the PO4 levels.

You folks just cannot measure it easily since it's used up before you can measure it(Bacteria-new rocks not yet established, macros, noxious algae, corals, Xenia etc), except at very high levels.

I was reading another thread about using Xenia as nutrient export. I hadn't realized that it would help all that much. Again something to research. I do have some Xenia (2 stalks) that I have had since the summer. It hasn't grown nor has it died. Maybe the same limitations??

I hope to do this with FW and SW systems in the coming months/year.

Regards,
Tom Barr

I hope you keep us informed on this research. It sounds like it could be applied to many of our tanks.

Vickie

 

[Plantbrain]

"The object, if I understand correctly, is to remove NO3 as the limiting factor and make PO4 the limiting factor. In that way the macroalgae would continue to grow until they ran out of PO4 which would reduce the PO4 from 0.03 (at present) to something less - maybe undetectable by the test kit. Sounds like a good way to go."

Nutrient limitation theory is directly explained in this manner from Liebig's law of limitation.

How can you have limited growth by limiting PO4, then say you have limited growth by NO3 at the same time?

You can pick one or the other, but not both for limiting the growth of something.

One will always be in excess relative to the other that is the limiting factor. Teetering between these two stresses things even further.

Plant growth and macro algae growth are directly related to N supply, not PO4 supply nearly as much, so the PO4 does not retard growth or cause uptake issues nearly as much as NO3/NH4.

This is why when I add KNO3, I do not get noxious algae and still have excellent macro growth. The NO3 levels at the lower ranges you feel are needed are limiting the macro algae, but not the noxious pest algae. They do fine at very low levels, so you are selecting for them, rather than the much larger macro algae.

This is seen in FW, SW, pelagic systems etc. The larger the organism is, the higher the concentration is need to have good growth.

A mouse and elephant, they both eat plants, which needs more food to survive? One reproduces very slow, the other rapidly.
This is similar to the small algae vs the large algae.

If you provide the things the macro algae need to use the PO4, then this can drivbe the macro algae to dominate the system for PO4. Then the PO4 is used up before the noxious algae have a chance to bloom and establish a foodhold.

"NH4 is ammonia, right?"

Technically ammonium, NH3 is ammonia, it's in this form when fish waste are produced or urea which is quickly converted into NH4 in water. NH4/NH3 are a ratio dependent on pH.

"I thought ammonia became NO2 (via bacterial action) which then became NO3 which had to be exported via water changes or broken down in the sand bed."

That's one way to export it, via the bacterial pathway, but there is a much better way: assimilate it into plant and coral tissue directly as NH4=> plant material. This short circuits the bacterial pathway and reduces the need for it, and can eliminate it almost entirely in optimized systems.

Macro algae are very good at removal of NH4, much faster and better than any bacteria. You can test how long it takes for a DBS to remove the NH4 dosed, vs a macro filled refugium.

"How do you "reduce NO3 to NH4"?"

The plant does this and expends energy to do this. NH4 on the other hand, requires no energy, it's already to be assimilated.

" Glutamine is food for plants or ??"

It is the organic form that NH4 is converted into in plants.

" Is this reaction taking place in the plants as opposed to the nitrogen cycle which takes place in the water?"

Well......inside the plant tissue(or algae). The bacteria do their reductions and oxidations inside as well, in a few cases on their cell surfaces, not really the water.

" Is that where I'm mixed up?"

Perhaps Sorry.


"The fact that I have seen an increase in macroalgae growth (since increasing my phyto added to the tank) tells me that I am adding some of the limiting factor (for macro algae growth). I'm just not sure what."

Well phyto is rich in N, it has some PO4 as well, you do not want to limit PO4 too much, then nothing will grow, ideally you maintain excess nutrients except for PO4, then as small amounts are dosed in via food etc, it's all snatched up by the macro algae.


"Our glass cages have many limitations. I am very conscious that the electric line ends at our house. In other words, whatever happens to this section, our electricity is affected. With this in mind, I plan on keeping to a lightly stocked tank so that the losses due to oxygen levels will be minimal. This does limit the amount of fish/critters I add to the tank but I had never thought that adding more livestock would reduce the PO4 levels."

You are wise to error on the light and easy side. Adding more livestock would add more N relative to P.
This would reduce the PO4 by reliving the N limitation.

But this has a limit since livestock adds NH4 directly first, then whatever is not used up quickly by the macros/noxious algae, will be NH4=>NO2->NO3 then perhaps used by the macro algae or else reduced in the DBS to N2 gas.

N cycling is not simple, many here the NH4=> NO2=> NO3 and then the NO3=> N2 gas thing and think that's all there is, but its not.

Xenia is a decent exporter, looks nicer to many than macros(depending on the macro and the Xenia so some use that. Macros are easy to maintain in some respects and export better.

It maybe limited some. I have not done studies on Xenia though, my work is only macros, microalgae and plants. It should behave positively to increases in N. You can chose to add it via the food(as NH4) or as inorganic forms in KNO3. It's a small tank, a water change will re set things so there is less to fear.

It's always fun to observe the unexpected.

Regards,
Tom Barr

 

[gatohoser]

Omg...so much info. I could only read the first post before i tuckered out. I will read this soon but heres a quick question...tho probably stupid.

Isnt sulfur an extremely risky and probably deleterious thing to ADD to an aquarium considering the main risk you take with a DSB is the production of hydrogen sulfide when it goes anoxic?

 

[Plantbrain]

Take a look at your salt mix, then tell me if you think having a Sulfur limited tank is going to work in a tank.......

At ~900ppm in natural seawater, I think that possibilty is remote..............

The reduction occurs when the Eh, the redox potential hits a certain range, this occurs when there is too much organic matter down there or too much nutrient loading for the bacteria. They cannot keep up with the supply of organic waste being added.

This occurs in estuaries and deltas and causes the swamp smells. Adding some carbon to prevent a limitation helps the start this off, but if you added too much organic carbon (eg dirt)., then the aerobic bacteria will quickly use up the O2 and remove virtually all of it. Some O2 removal is good, but not this much to cause SO4 reduction to H2S.

That occurs about (-)100 to (-)200 mv, Denmitrification occurs much higher, around 200-300mv.

Adding a little organic matter will cause the mv/redox to drop a little, adding a lot of OM....well, I think you get the picture.

Most tanks have low amounts of OM being added. Some die off from live rock curing etc contributes to this pool of carbon and is one of the main reasons it takes time for the rock to cure.

Once the bacterial colony is stable and use to the amount of available carbon and other nutrient source, then things run well.

If a system is overloaded with NO3 and not enough Carbon, then the DBS will not work as well.

If you too much carbon and not enough NO3, the reverse can occur and eventually you will have some Sulfur reduction......

Everything is a balance and you cannot go 100% one way or the other to have optimal results.

I think many assume less is better(nutrients, carbon etc) or more is better (light, Ca, KH) no, a balance is better.

How to achieve that balance is generally what folks are searching for to the road to success. Some want to know why or at least get some sense out of it to know it's not voodoo even if they don't understand all the mechanisms.

That's not required to do the "how".

Regards,
Tom Barr

 

[gatohoser]

Ok so it WAS a dumb question. But had to ask.

Very informative thanks!