Tetra Test Nitrite Kit is suitable for freshwater and marine aquariums and includes up to 45 tests Nitrite is produced from the breakdown of ammonia in the filter. Nitrite is highly toxic to fish, but is usually removed from the water by the bacteria which live inside the filter. However, in new tanks, or if the filter bacteria are damaged, the nitrite level may become toxic. Regular testing, especially in new aquariums, will prevent damage caused by nitrite poisoning. How it Works The TetraTest Nitrite kit is a liquid kit, which works by changing the colour of a water sample in relation to the nitrite concentration. You simply need to compare the colour of the sample to the easy-to-read colour chart in order to determine the nitrite level. How to Use In order to test the nitrite level, simply take a sample of aquarium water in a jug, and then use some of this to wash out the test vial. Then: 1. Fill the vial to the 5ml mark; 2. Hold nitrite reagent bottle number 1 upside down and add 7 drops, close vial and shake gently; 3. After 10 seconds add 7 drops of nitrite reagent number 2, close vial and shake gently; 4. Leave vial to stand for 2 to 5 minutes for full colour development. Compare the colour of the liquid to the nitrite colour chart to obtain the concentration. Always read the instructions carefully before use. If nitrite levels are high then you should seek advice as to the underlying cause.