Nitrite is produced when bacteria degrade protein and ammonium. It is normally processed further into non-toxic nitrate. In aquarium and pond water nitrite (NO2) should not be measurable. If nitrate is measurable, it is a sign that the bacterial degradation process has been disturbed.
From a concentration of 0.4 mg/l onwards it is dangerous or even fatal for fish, because nitrite blocks the transport of oxygen in the blood, so make sure you are regularly testing your nitrite levels using a test kit such as JBL's Pro AquaTest NO2.
To use, fill the glass vials with sample water, add reagents to one vial, place vials in holder and read values off the colour chart.
Usage: When setting up a new freshwater aquarium: daily for 3 weeks. For initial setup with marine water: once a week.
Box Contains: 1 nitrite test for approx. 50 measurements, incl. 2 reagents, 2 glass vials with screw caps, syringe, comparator block and colour scale.