Biological Filtration Or Cycling A Tank
An appropriate filtration system is a must in any aquarium if you want healthy fish and plants.
Broadly, there are three types of filtration that are available today – biological, mechanical and chemical.
While, if you have a marine aquarium you would pretty much need to have all three types of filtration for your tank, you can afford to take it easier if you have a freshwater tank, and pick any one of them. A biological filtration system (a natural filtering system consisting of helpful bacterial colonies that, through a cycling process, convert pollutants in water to harmless nitrate) comes into play even before introducing new fish into the tank, and once properly set up would continue after that as a cycle. Nitrate is nitrogen, therefore this cycling process is also referred to as the nitrogen cycle or cycling a tank.
When an aquarium is initially set up there is no biological filter present in the water because the colonies of bacteria responsible for it have yet to be established. When fish are added to the new tank they immediately begin to pollute the water with highly toxic ammonia exuded from breathing and waste. The water will look clean, but it is quickly becoming poisonous to the fish.
During the first 7-14 days ammonia will soar to deadly levels in a new tank, causing some fish to succumb and others to be weakened and take ill. Finally this overabundance of ammonia triggers the natural development of a good bacteria called nitrosomonos which feeds on ammonia, converting it through oxidation to nitrite.
While nitrite is less toxic than ammonia, it is still deadly to fish. For the next 10-14 days nitrite levels rise as more and more ammonia is converted, with new ammonia being converted as well. When nitrite builds to deadly levels, the last stage of the nitrogen cycle kicks in and nitrobacter, another good bacteria, spontaneously blooms to thrive on the toxic nitrite, converting it to harmless nitrate.
Nitrobacter takes longer to establish than nitrosomonos, so toxic nitrite will drop only slowly. But eventually both bacteria colonies will catch up to production, and keep up, canceling pollutants as they are created. When nitrite and ammonia levels both test at zero, and nitrate is measurable, the nitrogen cycle is complete and a biological filter has been established. This process of establishing the biological filter normally takes 4-6 weeks.
