What is nitrate?
Nitrate is produced by the beneficial bacteria in the water and filters as they break down the fish’s toxic waste products (ammonia and nitrite). Nitrate is not typically toxic to fish, but excessively high levels (>100mg/l) can cause problems with growth.
What is the correct nitrate level?
The level of nitrate is dependent upon a number of factors, including the nitrate level of the tap water (or spring water, etc) feeding into the aquarium, the number of fish, and the amount of food fed. High nitrate levels will lead to algal growth. A nitrate level of zero is ideal and implies a balance between waste produced by the fish and nutrients taken up by the plant life. Remember: this plant life does include algae.
What do I do if the nitrate level is wrong?
Maintenance of a zero level of nitrate is extremely difficult. Most domestic water supplies have a low level of nitrate. The key to the maintenance of low nitrates is regular water changes to dilute the build-up of nitrate. Also, increasing the higher plant life in the aquarium should use up nitrate. This will lower the amount of nitrate available to algae.