Review: Abdel Rahman El Gamal (Founder of the website)
The inserted pictures show substrates used in intensive aquaculture systems. As shown, the shapes of such substrates may vary although they have a main characteristic in common which is a high surface/volume ratio. Added to that, the substrates used in biological filters should enjoy strong mechanical resistance, limited clogging chances and of course its availability at affordable prices.
No matter what shape and contents of biological filters, its main function of the filter substrates is to create favorable conditions for the two bacterial colonies in order to perform the nitrifying process whereas Nitrosomonas sp. oxidize the ammonia to nitrite, and then Nitrobacter sp. complete the nitrification process through the oxidation of nitrites into nitrates bearing in mind that ammonia is the most dangerous part of the metabolic wastes produced by the fish while nitrate is almost not toxic to fish.
Biological filters are required in closed systems as it allows for the partial re-use of water as well as saving energy in case of heated water. In addition to reducing heating (or cooling) costs, such filters reduce the impact on the environment through the minimum water discharge.
Typically, a biological filter is submersed in a separate tank and colonized by nitrifying bacteria. In order for the filter to perform the nitrification process as planned, it requires stable physical and chemical parameters, a permanent supply of ammonia and adequate levels of oxygen. The biological filter is, within a re-circulation system, the more complex component, to the extent that it can be considered almost a living organism. As such it requires stable physical and chemical parameters, a permanent supply of food (ammonia) and adequate levels of oxygen.