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How to Cycle a Fish Tank

Ensure a healthy, balanced environment in your aquarium by following this simple process.


  • Step 1: Set up fish tank Set up your fish tank and filter system, then fill it with water.
  • : Avoid using water with chlorine.
  • Step 2: Stock with hardy fish Stock your tank with hardy fish, such as mollies, tiger barbs, white clouds, or guppies.
  • TIP: Hold off on goldfish; they are more vulnerable to disease.
  • Step 3: Limit the number Put in just a few fish. Three 1-inch fish are sufficient if your tank is between 10 and 20 gallons.
  • TIP: Adding too many fish will result in excess waste and stress the fish.
  • Step 4: Change the water Change 10 to 15 percent of the water every few days.
  • Step 5: Test a water sample Test a sample of the water after a week. It should test high in ammonia with a trace of nitrate at this time.
  • TIP: Ask the pet shop where you bought the fish if they'll test it. Many stores will do this for free or charge a small fee.
  • Step 6: Continue the process Continue moderate water changes every two weeks. Cycling a tank takes up to eight weeks. Your goal is to establish a healthy colony of bacteria that live in the filter, removing ammonia and other toxins from the water.
  • Step 7: Add more fish gradually Add more fish gradually, and enjoy watching them thrive as a result of your diligence.
  • FACT: The animals in the "Oceanarium" at Chicago's Shedd Aquarium consume over 650 pounds of seafood each day.

You Will Need

  • A fish tank
  • A filter
  • Hardy fish
  • Water samples

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