How to Flush Freshwater Tanks

When you have live freshwater fish, it can be deadly to perform a complete water change; instead, it is recommended that you change only 10 to 15 percent of the water at a time to avoid upsetting the habitat your freshwater fish have become accustomed to. However, if you're repurposing a freshwater fish tank which is no longer in use, you will have to flush it out completely to remove all the stagnant water, algae, bacteria and contaminants which have built up over time.

Things You'll Need

  • Buckets
  • Table salt and fresh water (or a premixed saltwater cleaning solution)
  • Chlorinated bleach
  • Dechlorination agent
  • Rubber basins for soaking aquarium accessories
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Instructions

    • 1

      Disconnect any active piping, tubing, temperature control units or pumps that service the freshwater fish tank. Remove these accessories from the work area to prevent the possibility of damaging them.

    • 2

      Drain the standing water in the tank into a bucket, if the fish tank has a built-in drain. If not, manually remove the water by dumping it down a drain; you'll need another person's help to do this if the fish tank is large and heavy. For unusually sized or especially heavy tanks, remove as much water as possible by dipping a bucket into the tank and pouring it down the drain until only a minimal amount of water remains; this will make the tank much lighter and easier to move.

    • 3

      Use a saltwater solution to clean out the tank if it is not heavily soiled. You can buy a premixed salt-based tank cleaning solution from your local aquarium hobby shop, or mix 2/3 cup of regular table salt with a gallon of warm water to get the right balance.

    • 4

      Fill the tank with the saltwater cleaning solution at let it sit for at least half an hour. For optimal results, leave it to sit overnight. Then, empty the tank and rinse it thoroughly with fresh water.

    • 5

      Use bleach rather than a saltwater solution if the tank was contaminated with parasites, algae or bacteria; it is a much more powerful cleaning agent. Mix chlorine bleach with water in a ratio of 20 parts water per every 1 part of bleach. Fill the tank with this bleach solution, and soak all the aquarium's filters accessories as well; 24 to 48 hours of soaking is recommended.

    • 6

      Rinse the tank and its working parts and accessories thoroughly with fresh water as well as a dechlorination agent after 24 to 48 hours of soaking. Do not pour this water down the drain, as it is potentially harmful. Instead, follow your municipality's procedure for the safe disposal of contaminated water waste.