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How to Create Beneficial Bacteria for Fish Ponds

| Updated September 26, 2017

Things You'll Need

  • Pond filter

  • Commercial beneficial bacteria

  • Chlorine remover

  • Rocks, stones or gravel

  • Water test kit

  • Goldfish or koi

Keeping a pond healthy means maintaining a healthy ecosystem. An integral part of the equation is a thriving colony of beneficial bacteria. Beneficial bacteria work by removing plant and fish waste before levels of ammonia and nitrates spike and kill the fish and plants.

Any new water that will be added to the pond must be treated with chlorine remover, which is available at most pet supply stores.

Buy a water test kit and test the pond. Beneficial bacteria, as well as plants and fish, need a particular water chemistry to thrive. The pH should be between 6.8 and 7.4, ammonia 0 to 1 parts per million, and nitrates under 5 ppm (see Reference 1).

If the pH level is off, commercial products are available to lower or raise it. After adding these products, test the water the next day. Continue to test the water twice a week.

Provide a surface for the beneficial bacteria to grow, such as rocks or stones, along with a filter. A pond should have a filtration system that contains a medium that will allow beneficial bacteria to grow, such as filter mesh or gravel.

After letting the filter run for a few days, buy beneficial bacteria from a pet store or a pond supplier and add it to the water. If another tank with a filter system is available, try rinsing the filter mesh in the pond water to introduce the beneficial bacteria.

Add tester fish like large goldfish or small koi to the pond, and some tester plants. Beneficial bacteria feed on fish and plant waste, so these must be added to keep the bacteria colony alive.

Continue to test the water after adding the tester fish. If the testers live, introduce one new fish at a time.


  • Do not clean the filter during the first month of starting the pond. This could kill the beneficial bacteria colony.