How to Keep My Freshwater Tank Clean & pH Down

The ideal pH conditions of a fish tank are dependent on the type of fish in the tank. Fish species such as the rosy tetra or Siamese fighting fish, do best in slightly acidic or low pH (below 7.0) waters. When the pH rises to a more alkaline state (above 7.0), problems can arise, even for more tolerant fish species. These conditions can cause the ammonia from the fish waste to become more toxic, according to "Freshwater Aquariums for Dummies." Ammonia and nitrate levels rise with the build-up of fish waste. Removing and replacing the tank water will usually improve water quality and lower pH. However, you do not want to make dramatic changes to your tank's chemistry as this will shock and kill the fish.

Things You'll Need

  • Sodium biphosphate
  • pH testing kit
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Instructions

    • 1

      Complete a partial water change of about 20 percent twice a month. This will replace the dirty water with clean water and help lower the pH as the fresh water usually has a pH of around 7.0.

    • 2

      Increase the water changes to once a week if the pH or ammonia levels are still too high. It is better to do small, partial water changes several times a month rather one large water change. Sensitive fish may not survive large water changes.

    • 3

      Add a pH-lowering solution that contains sodium biphospate (found at any fish retailer) to your tank if the gradual water changes are not affecting the pH as you need. Change the pH gradually following the directions. Fish expert Joseph S. Levine states in "The Complete Fishkeeper" that, "Changes in pH...should be made no more quickly than 0.1 units per day."

    • 4

      Add the pH-lowering solution with every water change if you live in an area with alkaline water (above 7.0 pH). How much to add will take time to determine through trial and error. Start by adding as little as possible and testing your water every day to measure the effects.