There are 3 key compounds in understanding of the nitrogen cycle in an aquarium. These are ammonia, nitrite and nitrate. 2 of those compounds are toxic to the fish whereas the other one is non-toxic. The biological filters or the nitrifying bacteria that lives on the biological filters help transform these toxic compounds to the non-toxic compound. This is called nitrogen cycle.
1. Ammonia
Ammonia, scientifically represented as NH3, is the output of the metabolism of the protein. The fish consumes the food, and the fish poop contains ammonia – it’s the waste product of the fish. Ammonia can be found in two forms. Un-ionized ammonia, represented as NH3, is toxic to the fish whereas ionized ammonia, represented as NH4+ is non-toxic to the fish. When you feed your fish and they poop, there is a mechanism to remove the ammonia dissolved in the water. That’s is called biological filter and the nitrifying bacteria that are housed on the filter. Ammonia is the main source of this nitrifying bacteria and the output of this consumption is Nitrite.
2. Nitrite
Ammonia consumed by the nitrifying bacteria creates nitrite as the product. Sadly, nitrite is toxic to the fish as well. It binds with the hemoglobin in the blood stream of the fish and creates methemoglobin. Hemoglobin carries the oxygen to the cells whereas methemoglobin does not carry any oxygen. So, increased amounts of nitrite in the aquarium will actually suffocate your fish. There’s another bacteria living on the biological filter that consumes nitrites and converts nitrites to nitrates.
3. Nitrate
Nitrate is non-toxic to the fish. Yay! Finally – thanks to the nitrifying bacteria breaking down the ammonia and the nitrite – we were able to get to a compound that is not toxic to the fish. In fact, nitrates makes the main food source of the live plants, just like fertilizers. Either you can have live plants that thrive on nitrate or you do regular water changes to keep the nitrate levels down. In nature, nitrate is converted into nitrogen gas by the denitrifying bacteria but that’s usually not the case for our home aquariums.
Bottom line is that nitrogen cycle is inevitable as the fish feed and poop. Investing in the nitrifying bacteria is key to a healthy ecosystem.