The second stage in the nitrogen cycle. As nitrifying bacteria are readily available they will build a colony as 
soon as the nutrient source (ammonia) is available.
While ammonia is being converted predominantly by the species of nitrosomonas, nitrobacter is mainly responsible for converting nitrite into nitrate. When setting up a new tank, the nitrogenous compounds will rise to high levels. This enables the bacteria to form a colony and to start the conversion process (nitrogen cycle).
Nitrosomonas and Nitrobacter are aerobic bacteria and need a constant flow of oxygen in order to survive and to perform their tasks.
Nitrite levels should be at an undetectable level at all times after the tank has fully cycled. Not as dangerous as ammonia, but still a highly toxic chemical, Nitrite causes stress for fish even as low as 0.5 ppm. Levels exceeding 10-20 ppm are lethal over a period of time. Immediate action is required if high nitrite levels persist after 7-10 days.
