Nitrogen/Phosphate chemistry of a clean up crew

[Mountain Reefer]

I am setting up a new build, currently with only 4 small fish. Feeding very very little, but still some food ends up in gravel. Told myself, time to order clean up crew to take care of the uneaten food. But that got me thinking. Does a CUC actually do anything in terms of nitrates and phosphates over simply letting food rot in tank. I know CUC useful for algae control, and maybe for "sand bed health", but do they really do anything positive in terms of tank chemistry over just letting bacteria decompose uneaten food?

 

[Lasse]

You bioload - the food you put in (if all the organisms you put in are still alive). Fish eat the food - around 20 % is converted into fish biomass - 80 % going out as waste. In the aquarium -> 80 % of the eaten food is waste - promote algae growth + uneaten food that will be converted into waste - promoting more algae growth. Ad CUC - they eat both uneaten food and the food internally produced - 20 % of this will be CUC biomass - 80 % as waste promoting algae growth - CUC eating again -> 20 % as CUC biomass -> 80 % as waste and so on.

Yes they are new feeding loops that help you to avoid that algae taking over and - yes - they will leave waste but it is not new waste - its is the result of your food you feed your fish with and in time they will reduce the waste in steps of around 20 %.

Let us say that you put in 1 g of P with your food. Fish will (if they are growing and young) convert 20 % as biomass (in the body) - 80 % coming out into the water as PO4 or organic PO4 - promote algae growth -> The CUC loop eat algae - convert around 20 % of the now existing 0.8 g P into CUC biomass - leaving 0.64 g to the next step - and so on.

Note this is just an schematic example - the figures do not need to be the absolute truth but this an example of a ecosystem that consist of many small feeding loops and I haven´t include the bacteria loops.

Sincerely Lasse

 

[Dan_P]

Great question. @Lasse conversion scheme provides a good way to think about how food and waste are processed. I will add that because every heterotrophic organism needs organic carbon just for energy production and only useS some for biomass generation, there will always be ammonia and phosphate left over. No matter how good a clean up grew, no matter what probiotic is used, ammonia and phosphate are left at the end of the scheme

After the ammonia is converted to nitrate, it accumulates along with phosphate. If the system is not overstocked, the nitrate is converted to nitrogen gas and the nitrate in the system remains low. Phosphate in an aragonite system will be low until the aragonite is saturated and then its concentration will begin to increase.

There are two ways to remove the excess ammonia/nitrate and phosphate: chemical and biological. The popular chemical means to remove PO4 include GFO and lanthanide phosphate precipitation. There are no effective chemical means for nitrate removal. The biological approach includes growing algae or growing bacteria. In both approaches energy is added to the system. For growing algae, light energy is supplied to a separate chamber to grow algae which assimilates ammonia, nitrate and phosphate. Harvesting algae removes the nitrogen and phosphorous from the system. For bacteria, chemical energy is added via organic carbon or sulfur addition. Removal of the bacteria occurs through skimming. A portion of the bacteria consumed by organisms in the system convert the bacteria to biomass and produce ammonia and phosphate. In the bacterial approach, a portion of the nitrogen and phosphate are accumulating in the system as biomass.

 

[Lasse]

It is IMO possible to recirculate all nutrients that have been put without exporting the outside world. It is a question of balance. With or without any refugium, If you have refugium and use macro species that will be eaten by fish - you just recirculate the harvest into the DT. If you use bacterial filter that you can backflush out to the aquarium water - you feed your corals with bacteria plankton. You can use your skimate in the same way. It is a matter of balance,

Sincerely Lasse

 

[Lasse]

needs organic carbon just for energy production and only useS some for biomass generation,

That´s true - but most of the losses (in a closed system) will come back as converted inorganic carbon into organic carbon through organisms that use photosynthesis through reuse of the CO2 that is the result of the energy production. These organisms (read algae) will be eaten.

Sincerely Lasse

 

[Randy Holmes-Farley]

I’m not actually sure how much of the N and P in food that “rots” gets back into the water. May not be more than when eaten by a fish. Most food molecules and particulates are not just chemically decomposing. They are being consumed in a variety of ways by microorganisms. Those microorganisms, like a fish, will use some of the N and P in the food to make their own tissues.

 

[Mountain Reefer]

I’m not actually sure how much of the N and P in food that “rots” gets back into the water. May not be more than when eaten by a fish. Most food molecules and particulates are not just chemically decomposing. They are being consumed in a variety of ways by microorganisms. Those microorganisms, like a fish, will use some of the N and P in the food to make their own tissues.

Thanks. Interesting. It may actually be better from a N and P point of view to let food be broken down by bacteria and then remove by skimmer over using CUC

 

[taricha]

...unless those bacteria team up in a cyano mat and hold a large amount of nutrients locally in patches in the sand.
Not all bacteria are skimmable.

 

[Lasse]

Thanks. Interesting. It may actually be better from a N and P point of view to let food be broken down by bacteria and then remove by skimmer over using CUC

Nope - not IMO - it will only be one loop - nature always works in many small loops.

I’m not actually sure how much of the N and P in food that “rots” gets back into the water. May not be more than when eaten by a fish.

Some will ends up as NH3/NH4 and PO4 in the mineralisation process - but with a healthy algae growth it will be bond in algae/plant or zoox biomass . These algae is eaten by the CUC and the loop starts up again. You will never be fast enough to rinse from bacteria biomass or mineralised N and P before the algae grab it as nutrients. Without algae eating CUC - you transform it into an algae problem. Without detritus eaters (like sea cucumbers) you will have a build up of organic matter. I have never siphon my sandbed in 4 years.

Sincerely Lasse

 

[Randy Holmes-Farley]

Nope - not IMO - it will only be one loop - nature always works in many small loops.


Some will ends up as NH3/NH4 and PO4 in the mineralisation process - but with a healthy algae growth it will be bond in algae/plant or zoox biomass . These algae is eaten by the CUC and the loop starts up again. You will never be fast enough to rinse from bacteria biomass or mineralised N and P before the algae grab it as nutrients. Without algae eating CUC - you transform it into an algae problem. Without detritus eaters (like sea cucumbers) you will have a build up of organic matter. I have never siphon my sandbed in 4 years.

Sincerely Lasse

In my system, detritus collected mostly in my dark sump and deep inside large rock filled refugia. It was up to an inch thick mud when I took it down. I presume uneaten food was among the materials collecting there, and algae in my main tank had no better chance of getting the loose N and P than did corals or any other organism in the system.

 

[Lasse]

The most interesting with my 4 years old tank is that I have not found any detritus traps yet. Not in my sump - (partly with stones) not below the chaeto in the refugium.

Sincerely Lasse

 

[Dan_P]

It is IMO possible to recirculate all nutrients that have been put without exporting the outside world. It is a question of balance. With or without any refugium, If you have refugium and use macro species that will be eaten by fish - you just recirculate the harvest into the DT. If you use bacterial filter that you can backflush out to the aquarium water - you feed your corals with bacteria plankton. You can use your skimate in the same way. It is a matter of balance,

Sincerely Lasse

It would be interesting to run such a system and discover whether balance is possible or would a “butterfly flapping its wings” cause the system to become unbalanced. How robust is such a balance I wonder?