How to Lower Nitrates in a Freshwater Fish Tank

When organic waste builds up in a freshwater fish tank, the nitrate level will increase. A high level of nitrates can be fatal to fish. High levels of nitrates can lead to a large increase of algae growth as well. Keeping nitrates at a proper level will reduce stress on fish and help keep your aquarium from becoming full of algae.

Things You'll Need

  • Nitrate testing kit
  • Aquarium vacuum
Show More

Instructions

    • 1

      Check the nitrate level of your freshwater aquarium with a nitrate testing kit. Nitrate testing kits can be purchased online or at pet stores. The goal is to keep nitrate levels under 10 ppm (parts per million), but most aquariums will be fine at levels from 10 to 40 ppm. Levels reaching 60 ppm will kill plants and cause stress on fish, which may be fatal.

    • 2

      Properly feed your fish to reduce nitrate levels. Uneaten food will break down in the water and cause higher levels of nitrates. Feed your fish twice a day instead of just dumping a large amount of food into the tank. Make sure your fish are eating all the food within a few minutes.

    • 3

      Change the water in your tank to reduce the amount of nitrates. How often you change the water in your aquarium will depend on the type of fish you have, but changing at least 20 percent of the water every month will help remove the waste products that have built up. If you change the water, but the nitrate levels are still too high after a day, change another 20 percent of the water until the nitrates lower to the appropriate level.

    • 4

      Clean your fish tank. Vacuum the gravel, rocks and decorations. Vacuums suction out waste products and dirt that collect in the tanks. Replace and clean filters and pumps, because uneaten food and other waste can be captured in those devices. Since nitrate levels increase when waste products break down, cleaning your tank is a major step in lowering the nitrate levels.