Elos No2 - Test Kit
The activity of the bio-filter in the aquarium system can be divided in mineralization and nitrification. The products of the mineralization process are ammonia and organic acids. The next step of decomposition is the oxidation (nitrification) of ammonia and ammonium to Nitrate (NO2). Nitrate has a toxic effect on fish because it oxidizes hemoglobin to methemoglobin. While hemoglobin is responsible for the transport of oxygen, methemoglobin lacks this ability!
Nitrate concentrations higher than 0.05mg/L (ppm) of NO2 are not acceptable for keeping aquarium fishes.
For these reasons, the periodical analytical valuation of nitrate in the aquarium water should be considered, especially during the aquarium set-up and periodically, to avoid the activity loss of the bio-filter system.