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How to Make a Fish Tank's Water Not Very Hard

Hard water is caused by high mineralization. Water hardness can be broken down into two components: hardness contributed by calcium or magnesium, or general hardness (GH) and water hardness related to the carbonate concentration in the water (KH). The carbonate concentration is related to the buffering capacity of your fish tank's water or the ability to prevent the pH from changing by absorbing hydrogen ions from the water.

Things You'll Need

Water hardness test kit

Instructions

- 1
  Determine if the water in your fish tank is hard because of the decorations or if the water you are filling the tank with is hard. Tank decorations such as dolomite, crushed coral and shells contribute to the water's hardness by dissolving carbonates into the aquarium water.
- 2
  Test the water hardness of your fish tank with the test kit. Test the water hardness of your tap water or other water sources that you usually put in the tank. If they are the same, you will have to find a new source of water for your tank, such as using deionized water for part of your water changes.
- 3
  Remove decorative shells and coral from the fish tank and do a quarter-tank water change. After 24 hours, retest the water in the tank and see if you have reduced the hardness.
- 4
  Replace dolomite or crushed coral substrate in the fish tank with a more neutral gravel, such as river pebbles. Test the water after changing the gravel and see if your water hardness has dropped.

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