Water Hardness in the aquarium
Hardness... and how to change it
The hardness of water is related to the dissolved minerals in contains. The total hardness is usually regarded as consisting of two components: general hardness (GH) and carbonate hardness (KH).
General hardness is caused by divalent metal ions, primarily calcium and magnesium.
Carbonate hardness is due to carbonate/bicarbonate ions, and represents the main 'buffering capacity' of the water, i.e. its ability to resist
pH changes. KH and pH are therefore inter-related: if KH is high, the pH will be very stable (and difficult to alter), if KH is low (e.g. less than 3 degrees KH) then the pH will be less stable.
ncreasing hardness is normally fairly easy. Adding decor to the tank which will gradually leach hardening salts (such as limestone rock) is one way. Hardening materials such as coral gravel could also be added to a canister filter. There are also commercially available hardening salts - these are often used for tanks containing cichlids from the African rift lakes, which are hard and alkaline.
Decreasing hardness can be done in two main ways: dilution with softer water, or adsorption of hardening ions. Some people use reverse osmosis (RO), distilled, deionised (DI) or rainwater to dilute their tapwater to a hardness suitable for their fish. Note that hardness has a fairly straight-forward relationship with dilution. For example, if your tapwater has a GH of 10 and you use half tapwater and half pure water, the GH will be 5.
There are also specific products designed to reduce hardness by absorbing the hardening ions. One natural product which can achieve this is peat, while also adding beneficial organic acids to the water. However, the quality and usefulness of different types of peat varies considerably.
