Looking for thoughts on organic carbon dosing and nitrate

[Randy Holmes-Farley Verified Community Expert]

I was more referring to " varibles" to affect a process. I don't think we have enough info about the denitrification in a tank yet. I wish I time and the proper equipment to observe . what else is happening that we cannot test for?

I certainly agree that different tanks will have different assortments of organisms using nutrients in different ways.

 

[Dan_P]

I certainly agree that different tanks will have different assortments of organisms using nutrients in different ways.

Thinking about ways to test the following reason for variable rates of nitrate reduction by carbon dosing.

The different rates of nitrate reduction observed in organic carbon dosing reflect the growth rate of bacteria that are consuming the carbon. I assume that the lag time is relatively small and the family (s) of bacteria is the same across aquaria. Growth rate increases as the amount of carbon relative to the bacteria population size increases. A small excess of organic carbon produces a small linear growth rate while a large excess permits near exponential growth. If the relative amount of carbon to bacteria declines, growth declines, approaching something like the stationary phase of a batch bacteria culture. This decline can occur if bacteria biomass accumulates because of inadequate skimming or mechanical filtration even though the dose size remains the same (I assume the bacteria are benthic and through biofilm dispersal are removed by skimming and filtration).

Is there a setup without a skimmer that can test this idea? Can the biofilm be harvested as a replacement for skimming? Then there is the question of determining whether low bacteria removal is causing low nitrate reduction rate in an aqyarium.

 

[1979fishgeek]

My experience is that following the recommended dosing instructions on various brands the no3 falls very fast. Usually too fast so I’d advise to start slowly and do half or quarter dose and test really regularly as it can suddenly bottom out or shock livestock.

It’s easy to see if dosing too much as white bacteria film becomes obvious on glass and can create cobweb looking slime on equipment first sign is water column becomes clouded.

I’ve found PO4 on the other hand can be quite stubborn to see dropping over a short time seems to take much longer.

Great topic!

 

[Koty]

I did not read all the posts, so sorry if I am repeating already-posted ideas. The first question is whether the dosed carbon is the rate-limiting step for bacterial growth. Another issue is that the carbon concentration fluctuates according to the number of doses. In the simple case of one dose, the concentration decreases exponentially, affecting the bacterial growth curve (regardless that the NO3/PO4 are rather stable). At the same time, the skimmer constantly eliminates a portion of the bacteria from the water column but not from the substrate-bound. Long term, this may be selected for carbon/PO4/NO3 assimilation by substrate-bound bacteria unless the same bacteria can proliferate in the water column and on substrates.
One thing to avoid is oxygen becoming a rate-limiting step. So my answer to the original question is that carbon concentration fluctuations and the skimmer may slow the process. Also, different and more complex rate-limiting steps include competition for the surface to grow on, a certain rare chemical or biochemical compound, and bacterial predators that rise after a short lag.
My experience is that although I use all possible export methods and quite a lot of carbon (2ml ElimiNP/100g dosed once a day), I seem to have reached the limit of carbon dosing where my PO4 is around 0.2 ppm and NO3 10-15 ppm.

 

[Randy Holmes-Farley Verified Community Expert]

My experience is that following the recommended dosing instructions on various brands the no3 falls very fast. Usually too fast so I’d advise to start slowly and do half or quarter dose and test really regularly as it can suddenly bottom out or shock livestock.

It’s easy to see if dosing too much as white bacteria film becomes obvious on glass and can create cobweb looking slime on equipment first sign is water column becomes clouded.

I’ve found PO4 on the other hand can be quite stubborn to see dropping over a short time seems to take much longer.

Great topic!

OK, that may sometimes be the case, and even is my expectation, but the premise of my question is why so many people find nitrate declines very slowly or not at all for a substantial period.

 

[Randy Holmes-Farley Verified Community Expert]

Thinking about ways to test the following reason for variable rates of nitrate reduction by carbon dosing.

The different rates of nitrate reduction observed in organic carbon dosing reflect the growth rate of bacteria that are consuming the carbon. I assume that the lag time is relatively small and the family (s) of bacteria is the same across aquaria. Growth rate increases as the amount of carbon relative to the bacteria population size increases. A small excess of organic carbon produces a small linear growth rate while a large excess permits near exponential growth. If the relative amount of carbon to bacteria declines, growth declines, approaching something like the stationary phase of a batch bacteria culture. This decline can occur if bacteria biomass accumulates because of inadequate skimming or mechanical filtration even though the dose size remains the same (I assume the bacteria are benthic and through biofilm dispersal are removed by skimming and filtration).

Is there a setup without a skimmer that can test this idea? Can the biofilm be harvested as a replacement for skimming? Then there is the question of determining whether low bacteria removal is causing low nitrate reduction rate in an aqyarium.

Just some musing related to your comments...

I agree the lag time is expected (by me) to be small ( a week or less) in an established reef tank with rocks and sand, etc., , and I don't think it really matters if the bacteria are the same or not since many species can use acetate and ethanol.

One idea is that maybe it isn't actually bacteria after all that are the prime users, but rather larger organisms that do not grow and expand very rapidly and that do not acquire N and P at the same rate that bacteria would, but rather store the gained energy in some fashion the way a person would (a person consuming a lot of ethanol or acetate will not add that much tissue that has new N and P, but rather as carbons tore means, such as fat and polysaccharides (e.g., glycogen), etc.

One question bearing directly on your premise is whether the amount of bacteria relative to the added organic carbon matters. It wouldn't seem to if all of the added carbon went into building new tissue, either for the energy needed or the actual biomolecules. Under that assumption 1 g of organic carbon results in X grams of taken up N and Y grams of taken up P (which may vary a bit by organisms, but not hugely so).

But if the amount of added organic carbon is low, and existing bacteria are nearly starving for organics, the taken up organic carbon might only be used for maintenance, with little or no expanded numbers of bacteria and little incorporation of N and P. Thus, it might be the case that adding 100 g of organic carbon takes up more than 100 times the amount of N and P than when dosing 1 g (at least if this is the only mechanism considered).

i don't know how readily one could measure biomass increase in a reef tank setting with lots of different microenvironments.

 

[Randy Holmes-Farley Verified Community Expert]

I did not read all the posts, so sorry if I am repeating already-posted ideas. The first question is whether the dosed carbon is the rate-limiting step for bacterial growth. Another issue is that the carbon concentration fluctuates according to the number of doses. In the simple case of one dose, the concentration decreases exponentially, affecting the bacterial growth curve (regardless that the NO3/PO4 are rather stable). At the same time, the skimmer constantly eliminates a portion of the bacteria from the water column but not from the substrate-bound. Long term, this may be selected for carbon/PO4/NO3 assimilation by substrate-bound bacteria unless the same bacteria can proliferate in the water column and on substrates.
One thing to avoid is oxygen becoming a rate-limiting step. So my answer to the original question is that carbon concentration fluctuations and the skimmer may slow the process. Also, different and more complex rate-limiting steps include competition for the surface to grow on, a certain rare chemical or biochemical compound, and bacterial predators that rise after a short lag.
My experience is that although I use all possible export methods and quite a lot of carbon (2ml ElimiNP/100g dosed once a day), I seem to have reached the limit of carbon dosing where my PO4 is around 0.2 ppm and NO3 10-15 ppm.

I'm confident that low O2 is not rate limiting for bacteria growth in a reef tank that has sufficient aeration to support aerobic organisms such as fish.

I'm also confident that organic carbon availability is rate limiting for organic carbon uptake in a reef tank that also has photosynthetic organisms since I expect that bacteria with a ready food source can compete with photosynthetic organisms.

It may well be that skimmers fit into this scenario is some fashion, but I'm not currently seeing how it can explain a long lag phase, whether there is little skimking or normal skimking or excessive skimming.

 

[taricha]

There may be a number of reasons why the observation that ~1 ml of vinegar/gal seems to be an approximate starting point for notable nitrate decrease with very little observed below that. Here's another in addition to Dan's and Randy's points about growth of new biomass being low below a certain carbon input level...
Above a certain amount of organic carbon input, you probably begin to significantly increase the volume of water that experiences a low oxygen condition. Under a low oxygen condition, the nitrate becomes a viable electron acceptor - "denitrification". This might dramatically change the amount of NO3 that gets removed in a way that might be hard to predict from one tank to another.

Experiment idea:
Water with no3 in separate bottles. Either no aeration, strong aeration, or low aeration - 1 bubble /2-3 seconds.

Could also track it over time, to check for @Dan_P proposed mechanism that the same amount of carbon input gives less and less bang for the buck as the bacteria population levels off.

 

[Randy Holmes-Farley Verified Community Expert]

There may be a number of reasons why the observation that ~1 ml of vinegar/gal seems to be an approximate starting point for notable nitrate decrease with very little observed below that. Here's another in addition to Dan's and Randy's points about growth of new biomass being low below a certain carbon input level...
Above a certain amount of organic carbon input, you probably begin to significantly increase the volume of water that experiences a low oxygen condition. Under a low oxygen condition, the nitrate becomes a viable electron acceptor - "denitrification". This might dramatically change the amount of NO3 that gets removed in a way that might be hard to predict from one tank to another.

Experiment idea:
Water with no3 in separate bottles. Either no aeration, strong aeration, or low aeration - 1 bubble /2-3 seconds.

Could also track it over time, to check for @Dan_P proposed mechanism that the same amount of carbon input gives less and less bang for the buck as the bacteria population levels off.

Excellent idea. I had not considered the possible expansion of the anoxic regions.

 

[Dan_P]

Just some musing related to your comments...

I agree the lag time is expected (by me) to be small ( a week or less) in an established reef tank with rocks and sand, etc., , and I don't think it really matters if the bacteria are the same or not since many species can use acetate and ethanol.

One idea is that maybe it isn't actually bacteria after all that are the prime users, but rather larger organisms that do not grow and expand very rapidly and that do not acquire N and P at the same rate that bacteria would, but rather store the gained energy in some fashion the way a person would (a person consuming a lot of ethanol or acetate will not add that much tissue that has new N and P, but rather as carbons tore means, such as fat and polysaccharides (e.g., glycogen), etc.

One question bearing directly on your premise is whether the amount of bacteria relative to the added organic carbon matters. It wouldn't seem to if all of the added carbon went into building new tissue, either for the energy needed or the actual biomolecules. Under that assumption 1 g of organic carbon results in X grams of taken up N and Y grams of taken up P (which may vary a bit by organisms, but not hugely so).

But if the amount of added organic carbon is low, and existing bacteria are nearly starving for organics, the taken up organic carbon might only be used for maintenance, with little or no expanded numbers of bacteria and little incorporation of N and P. Thus, it might be the case that adding 100 g of organic carbon takes up more than 100 times the amount of N and P than when dosing 1 g (at least if this is the only mechanism considered).

i don't know how readily one could measure biomass increase in a reef tank setting with lots of different microenvironments.

Would the “larger organisms” consuming ethanol and acetate be single cell or multi- cellular?

 

[Dan_P]

There may be a number of reasons why the observation that ~1 ml of vinegar/gal seems to be an approximate starting point for notable nitrate decrease with very little observed below that. Here's another in addition to Dan's and Randy's points about growth of new biomass being low below a certain carbon input level...
Above a certain amount of organic carbon input, you probably begin to significantly increase the volume of water that experiences a low oxygen condition. Under a low oxygen condition, the nitrate becomes a viable electron acceptor - "denitrification". This might dramatically change the amount of NO3 that gets removed in a way that might be hard to predict from one tank to another.

Experiment idea:
Water with no3 in separate bottles. Either no aeration, strong aeration, or low aeration - 1 bubble /2-3 seconds.

Could also track it over time, to check for @Dan_P proposed mechanism that the same amount of carbon input gives less and less bang for the buck as the bacteria population levels off.

I like the experiment. It sounds like a worthy rabbit hole to visit.

If the pelagic version does not seem to work, repeating it with a bottle coated with a biofilm might show results. I am thinking it would be easier to starve a biofilm of O2 than water though harder to measure the biomass in a biofilm.

 

[Randy Holmes-Farley Verified Community Expert]

Would the “larger organisms” consuming ethanol and acetate be single cell or multi- cellular?

Corals, sponges, algae, clams, etc.

 

[Dan_P]

Corals, sponges, algae, clams, etc.

HaHa,, in retrospect the answer should have been obvious.

 

[330Bob]

My carbon dosing is not aimed to "fuel" aerobic heterotopic bacteria growth - it is aimed to give anaerobic heterotopic bacteria that use NO3 as electron acceptor (in the absence of oxygen as electron acceptor and hydrogen as donator) a useful electron donator. Many studies around classic denitrification have shown that ethanol (C₂H₆O) is best suited for this. Hence I dose in the proximity of an anaerobic environment (below my DSB)

Sincerely Lasse

I like this answer. Maybe you could expand on it for me.
I use Bio Pellets but saw this Red Sea product NO3PO2

I've not see a good explanation on how it works. Normally in a aquarium you have wastes
- Fish eat = ammonia in the water = death
- A bacteria that is on every fish will convert ammonia to nitrite = less toxic
then a 2nd bacteria again on every fish (you don't have to find it) converts Nitrite to less toxic Nitrate
Nitrate = food for ugly green hair algae
What eats Nitrate?
- Plants - what is the by product?
- Anaerobic bacteria - low oxygen bacteria only found deep in poorly perfused rocks or deep sand beds.

How does Nopox help with aerobic bacteria ? What is the name of the bacteria it helps grow? How does this bacteria convert Nitrate and Phosphate to ??? Where does the nitrate and phosphate go? What is it converted to.

Also it seems a Pellet reactor would be best for the aquarium as it keeps the bacteria in one place with the output at the skimmer intake. Just dumping Denatured alcohol into the upper tank with the fish would seem to be promoting bacteria growth in a much less controlled way vs a pellet reactor which grows its colony separate from the rest of the tank.

All say have a strong skimmer. What if one had no skimmer at all? What would happen?

Just trying to understand whats actually going on, appreciate any clarity you can offer.

 

[GARRIGA]

Last cycle and my first attempts at carbon dosing. Others can draw their own conclusion but I've repeated this process a few times to get GHA at bay. Test tank has approximately 16 gallons and max dosage recommendation is 3 ml per 25 gallons. The 15 ml dosage was to test resulting bacterial bloom prior to adding fish as a stress test. Bloom lasted about a day. Have not done higher dosages with fish and one time did have them gasping at the surface but that also only lasted a day. Not going to repeat that again but I find it best to stress test and establish max boundaries. Do however still dose higher than recommended. Between 2 and 4 ml per day. Last was 4 ml per day which completely removed the GHA.

Only negative affects have been white bacterial slime that quickly recedes once dosing has seized. Las I dosed was mid February hoping to reestablish GHA to test a lower dosage to suppress the algae while still avoiding that white slime. Oddly, only thing thriving being red turf algae. Haven't tested since I stopped dosing and just waiting on the GHA to show. It's an experimental tank and don't see the need to check why things are going well. Perhaps my large comparative to volume media filter has now established denitrification but that's purely anecdotal. Added a G6 XR15 Pro set to full spectrum and full intensity to see if the goal is achieved.

Experimental tank is a 20H with 4' undergravel custom plate driven by a 75 tidal filter which I adjust flow from max to lowest trying to see if flow affects carbon dosing and it hasn't although was hoping a slower flow would induce denitrification yet since February it's been mostly at max. Go figure.

No sump. No skimmer. No mechanical filtration other than floss because I want clearer water. Same reason for GAC. No WC since September 2021 when started.

One caveat. Nitrites were tested randomly just to validate presence or absence and that might affect why I have such high nitrate readings. Testing with API because I don't need precision. Just approximate.

 

[Lasse]

What eats Nitrate?
- Plants - what is the by product?

1) Plants and algae convert NO3 (and other inorganic forms of N) into amino acids and proteins - with other words into biomass

- Anaerobic bacteria - low oxygen bacteria only found deep in poorly perfused rocks or deep sand beds.

2) Beside the the same thing (as for plants and algae) - some anaerobic bacteria use NO3 in the metabolism as electron acceptor in the citric acid cycle (instead for O2) - waste N2 gas if it works well N2 and NO2 if it not is working as good as it can

How does Nopox help with aerobic bacteria ? What is the name of the bacteria it helps grow? How does this bacteria convert Nitrate and Phosphate to ??? Where does the nitrate and phosphate go? What is it converted to.

3) Please see the answer for plants and algae

Also it seems a Pellet reactor would be best for the aquarium as it keeps the bacteria in one place with the output at the skimmer intake. Just dumping Denatured alcohol into the upper tank with the fish would seem to be promoting bacteria growth in a much less controlled way vs a pellet reactor which grows its colony separate from the rest of the tank.

4) may be that way - but it could also be the other way around - an uncontrolled growth

All say have a strong skimmer. What if one had no skimmer at all? What would happen?

If you aim to fulfill the case number 3 - IMO you need a skimmer. But if your goal with the adding of DOC is number 1 - you do not need a skimmer the sam way - IMO - but I always prefer a skimmer in order to withhold a high =2 conce3ntration in the tank

Sincerely Lasse

 

[Randy Holmes-Farley Verified Community Expert]

How does Nopox help with aerobic bacteria ?

I do not think that reefers have much info on what types of organisms use the organic compounds dosed (vinegar, vodka, NPOOX, sugar, etc.) to a typical reef aquarium. Could be any combination of aerobic bacteria, hypoxic bacteria, corals, clams, sponges, etc.

Both hypoxic and aerobic bacteria, and likely higher organisms such as corals and sponges, consume the organic matter in NOPOX or other organic carbon dosing, and grow to build tissues, which incorporate N and P from the water.

Hypoxic bacteria can also use nitrate to get energy, along with the NOPOX, to make N2.

 

[Timfish]

How about being converted into a form that's not tested for or being sequestered by organisms we can't see or don't pay attention to. De Goeij showed nitrogen enriched detritus can start showing up in about a day after being consumed by sponges. Biofilms are another variable and can be sequestering carbon, nitrogen and phosphorus as well. From what I've seen over the decades is it can take a long time between when something is done and when the equilibrium of a system actually shows an observable change.

 

[biom]

I do not think that reefers have much info on what types of organisms use the organic compounds dosed (vinegar, vodka, NPOOX, sugar, etc.) to a typical reef aquarium. Could be any combination of aerobic bacteria, hypoxic bacteria, corals, clams, sponges, etc.

Both hypoxic and aerobic bacteria, and likely higher organisms such as corals and sponges, consume the organic matter in NOPOX or other organic carbon dosing, and grow to build tissues, which incorporate N and P from the water.

Hypoxic bacteria can also use nitrate to get energy, along with the NOPOX, to make N2.

Corals in their natural environment are dissolved organic carbon (DOC) net positive. About 40% of the photosynthetically fixed carbon by zoox is excreted by the coral in the surrounding water as mucus. I would expect it is like this in the aquariums too. Corals will probably take some of the carbon dosed as acetate but will release back much more as mucus. Actually this could be the reason why I dont need to dose organic carbon to lower nitrates and phosphates in my tank full of corals - the corals themselves are dosing enough

 

[Randy Holmes-Farley Verified Community Expert]

How about being converted into a form that's not tested for or being sequestered by organisms we can't see or don't pay attention to. De Goeij showed nitrogen enriched detritus can start showing up in about a day after being consumed by sponges. Biofilms are another variable and can be sequestering carbon, nitrogen and phosphorus as well. From what I've seen over the decades is it can take a long time between when something is done and when the equilibrium of a system actually shows an observable change.

That certainly happens. N gets incorporated into many biomolecules such as proteins. But If it is a proposed explanation of a delay in seeing nitrate drop when organic carbon dosing, I'm not sure i see how it is an explanation.