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