Nitrate is produced from the breakdown of nitrite in the filter. Nitrate can be harmful for marine fish, and high levels may indicate a general decline in aquarium conditions. The only way to know what the nitrate level is, is by testing it with a TetraTest Nitrate kit. Regular testing will help you to assess the overall health of the environment. How it Works
The TetraTest Nitrate kit is a liquid kit, which works by changing the colour of a water sample in relation to the nitrate concentration. You simply need to compare the colour of the sample to the easy-to-read colour chart in order to determine the nitrate level. How to Use
In order to test the nitrate 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 nitrate reagent bottle number 1 upside down and add 14 drops, close vial and shake gently;
3. hold nitrate reagent bottle number 2 upside down and add 7 drops, close vial and shake gently;
4. Add 1 spoonful of powder to the test vial, using the enclosed dosing spoon, close vial and shake well for 20 seconds;
5. hold nitrate reagent bottle number 3 upside down and add 7 drops, close vial and shake gently.

Allow 10 minutes for the colour to develop, and compare it to the enclosed colour chart. If nitrate levels are high then you should seek advice as to the underlying cause.