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Beginners Fishkeeping

The Aquarium Water Hardness

How does water hardness affects your aquarium?


The Aquarium

Water hardness relates to the amount of disolved minerals in the water. In the aquarium water hardness is measured two ways.

The first measure is General Hardness (GH)

The second measure is Carbonate hardness Hardness (KH)



Carbonate hardness is caused by carbonate and bicarbonate in the water. Because these can be removed by various processes, this is known as "temporary hardness". Carbonate hardness acys as PH buffer; if the water has a high carbonate hardness, it will have a very stable PH value, and addition of chemicals affecting PH will have limited action. Conversely water with a low Carbonate Hardness is very sensitive and PH will change very quickly.

General Hardness is the measure of the amount of magnesium and calcium ions in the water. It's General Hardness we're referring to whwn we talk about living in a hard water area.


Most UK tap water hardness is within a range tolerated by most tropical fish, so beginners are advised not to worry to much about hardness.