How do carbohydrates get cycled?

[confused_aquarist]

I’m not too sure if I understand fish tank cycling. Fish food protein is converted to nitrogen gas and hydrogen sulfide through several different reactions, where some bacteria may use nitrogenous waste byproducts as electron acceptors to store energy. The waste eventually becomes gas.

What about carbohydrates? Where will they end up? Are they consumed by the beneficial bacteria? Are there free-floating amino acids or nitrogen sources that will support growth of such beneficial bacteria? If much of the nitrogen will become gas, then it seems there will be a lot of imbalance if some organism is not busy clearing up or incorporating carbons preferentially. They could break down all the sugar they need but eventually there will be an endpoint because all of the available acceptor is degassed and there is not enough nitrogen to generate new protein.

If organic matter keeps accumulating, it would not seem to be a wise choice to skip water changes even when nitrates are kept to minimal or none.

 

[confused_aquarist]

I may have answered my own question. I guess that if nitrogen is limited, then much of the rest is rendered unusable/practically inert anyway?

 

[10 Tanks]

Hello. My understanding is simple sugars are used quickly, so pass through the body through urine. More dense carbs, like grains are used more slowly, so those would pass through the body as solid waste. Everything dissolves in the tank water and that's why water is referred to as "The Great Dissolver". That's why you must remove and replace a lot of tank water and do this frequently.

10

 

[TwoTankAmin36]

This from New Life Sectrum may help. Carbohydrates & Fats in Aquariums

 

[confused_aquarist]

Thank you!
I was mostly wondering about what the end products would be, how they're processed by decomposers and bacteria and whatnot, rather than how the animals process them.
One would think if tropical fish don't use carbohydrates efficiently then there would be an excess of carbohydrates in the environment.
But if bacteria cannot multiply when limited for protein/nitrogen source, then the excess carbs would practically be inert and wouldn't cause harm no matter how much they accumulated in the tank. After all, much of the nitrogen from diet (if not all) goes back to air, like how some of the carbs go back to air in the form of CO2. The bacteria can't use the carbon if they don't get enough nitrogen. Or could it be that they can fix nitrogen from atmospheric air.

 

[JakeKM]

Carbohydrates are used by heterotrophic bacteria. The traditional nitrifying bacteria in the biofilter are autotrophic and use atmospheric CO2 to produce sugars. And nitrogenous waste from fish food is not converted to nitrogen gas, it becomes nitrate. It's only converted to nitrogen gas in the absence of oxygen with an organic carbon source.

 

[confused_aquarist]

Carbohydrates are used by heterotrophic bacteria. The traditional nitrifying bacteria in the biofilter are autotrophic and use atmospheric CO2 to produce sugars. And nitrogenous waste from fish food is not converted to nitrogen gas, it becomes nitrate. It's only converted to nitrogen gas in the absence of oxygen with an organic carbon source.

I think what is happening in most of my tanks is that nitrogenous waste is indeed converted to nitrogen gas (by anaerobic bacteria), through an intermediate nitrate-generating step. This is because when I cycled my tank, I had lots of plants. Going from 5~10ppm nitrite to 0 ppm nitrite took about a month, and a 25(!)ppm nitrate peak immediately followed. It took 2 days for the nitrate to go from 25 to 0. I doubt this could've been achievable with plants only.
Because many anaerobic bacteria exist in seemingly aerobic surface biofilms, I don't think it's impossible for my filter media to house anaerobic bacteria. There may not be many of them, but there may be enough.

I didn't know that inorganic carbon was used by nitrifying bacteria. My impression was that nitrifying bacteria would use ammonium or nitrite as energy source. But I guess they have to derive carbon biomass from somewhere. If nitrogen source is either gassed off or absorbed by plants, it must be a limiting nutrient. How heterotrophic bacteria would survive in such low nutrient condition with supposedly tons of extra carbohydrates is what I don't really understand.

Or I guess there might not be excess carbon anyway and it all balances out in the end. Maybe the carbon breathed out by heterotrophic bacteria is used by nitrifying bacteria, etc. It's just hard to understand it when the whole process can't be easily visualized.

 

[TwoTankAmin36]

Nitrate in aquariums can be converted into nitrogen gas-N2 by facultative bacteria. These can use oxygen when iyt is present. but if there is a lack of oxygen in the water reaching them, then they can convert to using nitrate. When they do this part of the result is notrogen gas.

How this can happen is that in some pathways through biomedia (there are a lot of these), the nirifiers can use uo all the oxygen. The output is nitrate, When the water without O leaves the region of the nitrifiers and continues moving, what arrives at the place where any facultative bacteria are, they simply switch to using it since there is no O.

Plants preferred form of nitrogen in a tank is ammonium. The AOA prefer ammonia. Ince the cycle kicks in 100%, there is no longer enough total ammonia being creted to supply the plants with the amount of ammonium they neew. But plants can also use the nitrate produced by the nitrifiers. No matter how many plants are present in a tank there will alway be a bit of ammonia for the bacteria, So there will be some of these present even if the number are small.

When the plants use the ammonium, they do not make nitrite or nitrate. what all of this means is if one is trying to do a fishless cyle in a tank with live plants there results one gets from testing will not follow the same pattern as they do when there are no plants. Trying to determine what the results if cycling a planted tank should be is next to impossible as it all depends on how many plants of what size and species there are in the tank.

We do know things like floating plants can use atmospheric CO2 which gives them an advnatahe over submerged plabts which rekio on the CO2 dissolved in the water. Of course some plants can also use cabobonates or bicarbonates just as he nitrifying bacteria can.

It is relatively easy to measure the presense of ammonia, nitrite and nitrate is is another to determine what is consuming is and at what rate in a cycled tank with both nitrifying bacteria and an assortment of plants. Plus there are other bacteria which can also use ammonia.

Our tanks are a fairly complex ecosystem. Analysing 100% what exactly is in the water and what may be using and how would reruire a very well equipped lab to determine. And then it also requires one has the requisite knowledge to deal with and understand it all.

 

[confused_aquarist]

I'm so interested in how local oxygen concentrations can impact the anaerobic/aerobic bacterial compositions!
There are many reactions, like the hydrogen sulfide detoxifying reaction or carbon cycling reactions that aren't commonly mentioned.
I would think that there are some toxins, other than nitrogenous waste, that would be harmful for fish even in tanks that are seemingly cycled.
Creating a mature tank would probably require a wide bacterial repertoire.