How to Lower the KH in an African Cichlid Tank

Carbonate hardness, or KH, is a measurement of the carbonates and bicarbonates in water. It buffers water against sudden drops in pH, which typically happen as fish release acids from metabolic waste into the water. The carbonate hardness for a Rift Lake aquarium is normally in the range of 180 to 240 parts per million. Depending on the specific carbonate hardness test that the aquarist performs, the measurement may be in German degrees of hardness, and in this case, the ideal reading will be between 10 and 14 DH.

Things You'll Need

  • Dip-and-read carbonate hardness test kit
  • Deionized water
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Instructions

    • 1

      Observe your fish closely every day. By understanding their behavior and by knowing what healthy fish look like, you will quickly become aware if the water chemistry has shifted out of the optimal range, as the fish will behave differently and may exhibit difficulty breathing or display subdued colors.

    • 2

      Use a dip-and-read carbonate hardness test kit to determine the KH of your water, particularly if the fish are behaving differently. A reading of 198 to 240 parts per million is perfect for an African cichlid aquarium.

    • 3

      Use the dip-and-read carbonate hardness test kit to determine your tap water, if the KH reading is too high. Depending on where you are living, the main's water may be very high in dissolved minerals, which are elevating the KH of your aquarium water beyond optimal levels.

    • 4

      Remove some shells from your aquarium, if you are using aragonite sea sand or a crushed coral substrate and have numerous sea shells in the aquarium as well. Aragonite and crushed coral leach carbonates and other minerals into the water, as will sea shells to a lesser degree. If your carbonate hardness is too high, remove some of these natural materials, which are contributing to the elevated reading.

    • 5

      Use deionized water to dilute the original water in the aquarium. Remove five percent of the water and replace with deionized water, which is available from your aquatic dealer. Fish are highly sensitive to quick and drastic changes to water chemistry, so it is always best to make the necessary changes as slowly as possible.

    • 6

      Use the dip-and-read test kit to test your water after the first dilution. Continue to replace five percent of the original water with deionized water, until the KH has been lowered to the correct range.