dH, GH and KH... What is the differance?

[larmer120]

When I look up fish profiles, for compatability, I always see dH used to describe water hardness. Is this GH or KH? Is there another method of determining hardness that I don't know of? I have a "Tetra" test kit that tests for GH and KH. My GH is 9 and KH is 5, acording to the kit, that's fine for most fish. But I would like to understand better, so I don't make a "fatal" mistake.

 

[Bol]

To the best of my knowledge...

dH -- "degrees of hardness", sometimes called a "German degree". I don't know the reasoning behind this, but when talking about hardness, one degree equals 17.86 ppm. I'm not sure, but it seems that most times I've seen 'dH' used, it's with regard to GH.

GH - General Hardness. This is a measure of certain dissolved salts in your water -- mostly calcium and magnesium. General Hardness is what people are talking about when they mention "hard water" or "soft water".

KH - Carbonate Hardness. This is a measure of carbonate and bicarbonate ions in your water. The reason KH is important (arguably more important than GH) is because KH is related, chemically, to pH. KH is often called "total alkalinity".