How to Bring Down the Nitrate Level in an Aquarium

Thriving aquariums require appropriate and consistent nitrate levels.

Thriving aquariums require appropriate and consistent nitrate levels.

To keep your fishies healthy and icky algae growth at bay, keep your aquarium's nitrate level below 20 parts per million. Invertebrates need nitrate levels below 5 ppm and coral need it below 1 ppm. Any quality water testing kit for home hobbyists allows you to monitor the nitrate level.

Make only one effort to lower your aquarium's nitrate level at a time, waiting a few days to one week between tactics. Your finned friends and other aquatic life are more likely to become dangerously stressed by sudden major water chemistry changes than by levels gradually drifting too high.

Replace 10 percent of your aquarium water, or up to 15 percent if your nitrate level is considerably elevated. Do exactly what you do when you perform your usual water changes every two weeks or so, including all the same water treatments and temperature adjustments.

Purchase biopellets from your trusted fish supply source and add them to the tank as instructed by the manufacturer. Biopellets are a relatively new aquarium technology harnessing the natural power of beneficial marine microorganisms. The pellets dissolve in the water, and all the microscopic critters inside feast on nitrate and other undesirable water components.

Clean out your tank filtration system and protein skimmer. If you don't have a protein skimmer, get one. Clear the water of floating stuff with your aquarium net and run your substrate vacuum thoroughly over the bottom of your tank. These cleaning efforts remove detritus that releases nitrate into the water.

Put cured live rock or live sand in your tank. These serve as decoration or substrate, but do a lot more for your aquatic environment. Like biopellets, live rock and live sand contain microorganisms that chow down on nitrate. They also help keep your aquarium water crystal-clear and even provide nourishment to any of your little swimmers inclined to nibble on them.

Pick up one of the many denitrators available from your favorite fish supply store. All sorts of products are made to lower your nitrate level to restore balance and harmony to your underwater habitat. Use as directed.

Items you will need

  • Biopellets
  • Protein skimmer
  • Net
  • Substrate vacuum
  • Live rock or live sand
  • Denitrator


  • Because different denitrator products employ different methods and have varying efficacy, and because they can affect other aspects of your water chemistry, test your water frequently when using these things until you know for sure exactly what they do.
  • Get a product recommendation from your vet or another trusted source before making a purchase.

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About the Author

Eric Mohrman has been a freelance writer since 2007, focusing on travel, food and lifestyle stories. His creative writing is also widely published. He lives in Orlando, Florida.

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