Nitrification is the hidden magic that underlies every successful aquaponics system. It purifies toxic fish waste, (ammonia), and generates a continuous supply of healthy, organic plant nutrients, (nitrates).
A Two-step Process
Nitrification is fundamentally a two-step process. The first stage involves the conversion of the ammonia that is produced by the fish into nitrite. The details of the chemical reactions are shown below. Note that for this to occur there must be oxygen present.
The second stage of nitrification is the conversion of the nitrite into nitrate. This is shown in the reaction below
Again note that oxygen is also required for this phase, although not as much.
The importance of these two stages is dependent upon the fact that nitrite is considerably less toxic to fish than nitrite and nitrite less toxic than nitrate Whereas the recommended maximum concentration of ammonia is is around 0.02 mg/litre that of nitrite is ten times as high at 0.2mg/litre. Nitrate, on the other hand can be tolerated by most freshwater species at levels of 200+ mg/litre.