For the determination of the nitrite and nitrate concentration in freshwater and saltwater. Nitrite (no2-) is the intermediate stage of the aerobic nitrification and is highly toxic for fish and invertebrates. A too high concentration of nitrite - for example, caused by new filter material - impedes the oxygen transport in the blood and severely restricts cellular respiration. With this test, the nitrite content can be accurately determined from 0.01 to 2 mg/l with the finely tuned color chart.