This is a page detailing current knowledge of nitrifying bacteria, gleaned from scientific papers on nitrifying bacteria in both waste water management and aquarium systems. I’ll summarise...
1. The optimum level of ammonia for nitrifying bacteria is 400ppm. The upper limit is 2750ppm.
2. The optimum level of nitrite for nitrifying bacteria is 200ppm. The upper limit is 7500ppm.
3. Nitrifying bacteria need at least 80% oxygen saturation to thrive. Because of this, 80-84% of these bacteria reside in the filter. In a very clean, well filtered aquarium this proportion is even greater.
4. Nitrifying bacteria will survive for several years without food. They only need water and oxygen to survive.
5. Nitrifying bacteria colonies do not grow to a size governed by the bioload/amount of ammonia available. Since they don’t need to eat to survive, the colony continues to reproduce with the ammonia produced by fish. They will only stop reproducing if zero ammonia is available to them.
6. The brown ‘mulm’ that accumulates in a filter should not be removed (unless absolutely necessary to preserve water flow). It is full of bacteria, archaea, flagellates, ciliates, microscopic worms, and many other organisms. This mulm is largely composed of extracellular polymeric substances (EPS) secreted by the bacteria that house these organisms.
7. Nitrifying bacteria do not need KH. In even a very heavily stocked aquarium they get all the carbon they need from carbon dioxide.
8. There’s no such thing as a ‘bacterial bloom’ in the water column. These are in fact blooms of infusoria, feeding on heterotrophic bacteria.
9. Nitrifying bacteria cannot use ammonium (NH4-). This is why nitrification slows down in acidic water and stops at pH6, because ammonium is virtually non-existent at pH6.