How to Adjust Nitrates in an Aquarium

High levels of nitrates in a fresh or saltwater tank lead to algal blooms and, more seriously, can poison your fish. Nitrates appear naturally in the tank from fish feces and decomposing foods and are removed by plants and algae. In such a small environment, you need to keep nitrate levels under control through water changes. In certain circumstances--for example, when keeping giant clams--you do need a certain amount of nitrates in the water. Increasing nitrate levels artificially is possible but must be approached with caution to avoid killing tank inhabitants.

Things You'll Need

  • Nitrate test kits
  • Gravel cleaner
  • Bucket
  • Aquatic plants
  • Nitrate supplement
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Instructions

    • 1

      Test nitrate levels weekly with a test kit per the instructions. If you have a new tank or keep particularly fragile creatures, consider testing more frequently. Normally, nitrate levels should be close to zero. Levels below about 25 ppm are fine in most tanks.

    • 2

      Conduct regular partial water changes. Replace 10 percent to 25 percent of the tank water with fresh, filtered, dechlorinated water weekly. Make the water up with a salt mix if you have a marine tank. If nitrate levels climb, conduct larger or more frequent water changes.

    • 3

      Introduce more aquatic plants to your tank. These help keep nitrate levels under control.

    • 4

      Switch on the tank light for around 12 hours a day, which supports the growth of the nitrate-absorbing aquatic plants and algae.