Starting a Fish Tank Filter

There are a lot of different types of fish tank filters, but the most important thing they all do is harbor nitrogen-eating bacteria that convert the ammonia from fish waste and uneaten food into nitrate. Starting a filter is more involved than just plugging it into the wall. It takes about a month for bacteria to settle into the filter and establish themselves.

Things You'll Need

  • Fish tank filter (fully set up and installed in the tank)
  • Source of ammonia
  • Aquarium testing kit (with tests for ammonia, nitrite and nitrate)
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Instructions

    • 1

      Start your filter running by plugging it in. Ensure that the tank water is flowing smoothly through it. For example, for canister or power filters, water should be going into the intake and out from the outflow.

    • 2

      Add a source of ammonia to the water. Traditionally, people used hardy fish like zebra danios for freshwater tanks or damselfish for saltwater tanks. However, you can get the same results without potentially making fish suffer by using small amounts of fish food every 12 hours, a small piece of dead fish or shrimp, or drops of commercial 100% ammonia every day. For 100% ammonia, start with five drops per ten gallons of water, then add more if you don't see any with your test kit. Once you've worked out how many you need, use the same amount every day.

    • 3

      Test the ammonia level in the tank daily until it disappears. Put some of the tank water into a clean test tube or other small glass container, then either add the liquid test drops or dip in the plastic dipstick, depending on what kind of test kit you have. Wait a few minutes, then compare the color to the provided chart. (If you have a different type of test kit, follow its instructions.) The ammonia should rise and come to a peak, then decrease after one or two weeks. If you're using live fish as your ammonia source and the levels become very high, you can reduce the ammonia, which could endanger the fish, by removing half of the tank water and replacing it with fresh dechlorinated water.

    • 4

      Test the nitrite level daily once the ammonia levels have started going down. You should notice a spike at some point during the second or third week. If the levels are very high, or if the spike fails to go down, change out half the water to reduce it. Nitrite is also toxic to live fish, and even with fishless cycling, too much ammonia or nitrite will cause the bacteria to grow too fast, which reduces oxygen and ultimately slows down the tank cycling process.

    • 5

      Test for the presence of nitrate once the nitrite level has started going down. In most tanks, nitrate is present after about a month. Once you have some, it means the tank has fully cycled, your filter is populated with the right bacteria, and you can stop adding supplemental ammonia. When ammonia and nitrite are both zero, you can start adding new fish.