How to Cycle My Goldfish Without Killing Them

Cycling a fish tank helps create a toxin-free environment in which goldfish can live. In the wild, ocean currents and marine life continually refresh the water. In a tank, the ammonia in a goldfish̵7;s own waste can build up and poison and kill these animals. A new tank needs bacteria that feed on ammonia. These bacteria convert the ammonia to nitrites and then to nitrates, the latter of which does not harm goldfish. Owners only need to cycle a new tank once.

Things You'll Need

  • Ammonia testing kit
  • Nitrate testing kit
  • Goldfish tank
  • Filter
  • Heater
  • Light
  • Decorations (stones, figurines, pebbles)
  • Log book
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Instructions

    • 1

      Set up the new tank by adding stones and pebbles to the bottom of the tank. Add figurines and decorations as desired. Install the filter, heater and light and plug these into a wall outlet and then fill the tank with clean water.

    • 2

      Add goldfish to the clean water in the new tank after 24 hours. This period allows the tank to settle and the filtration system to remove any chlorine from the water. Let your goldfish swim in the tank for another day before testing the water, feeding them as necessary while waiting.

    • 3

      Test the ammonia and nitrate levels and write these numbers in your log. Testing kits may consist of vials and a chemical solution or paper strips treated with a chemical solution. Follow the instructions on the package to determine the concentration of ammonia and nitrates in your tank, which the kits can read in units of milligrams per liter (mg/L), parts per million (ppm), or by reference to a color-coded chart included with the kit.

    • 4

      Determine if you need to change the water by following the directions on the kit. As a general rule, if the ammonia level registers at 1.0 ppm or above, you need to change the water to avoid poisoning your goldfish. The ammonia starts to poison and kill goldfish at levels of 2.0 ppm and above and may even kill at 1.0 ppm.

    • 5

      Change the water if the ammonia or nitrite level rises above the safe levels indicated by the testing kit. Ammonia and nitrite levels below .25 ppm are safe for fish; for levels between 0.25 and 0.5 ppm, remove about 10 to 20 percent of the tank̵7;s water and replace it with fresh water. If the ammonia or nitrate levels reach 0.75 to 1.0 ppm or higher, remove as much as 70 or 80 percent of the tank̵7;s water and replace it with fresh water.

    • 6

      Continue testing and replacing water until the ammonia and nitrate levels approach zero. A new tank can take from 10 to 30 days to cycle, depending on the water temperature and other factors.