GH (general hardness) is the total hardness, measuring the total amount of
calcium and magnesium. To get the amount of each, you need to have a
calcium hardness test or a calcium test. The proportions of calcium to
magnesium are important for hydroponics, since plants need both calcium and
magnesium, in certain proportions to get the best growth, and with a total
lack of either, the plants will not grow.

KH is the carbonate hardness, which isn't really a hardness, but a buffering
capability.

Hardness, unless otherwise specified could be either, but I would expect GH.

Personally, the only one that I worry about is the KH.
--
RichToyBox
http://www.geocities.com/richtoybox/pondintro.html


"R&B Thomas" wrote in message
...
Hi,
I haven't written in a while so bear with me. I am going to purchase
some
Hardness Test Kits and would like some input from this newsgroup. I'm
contemplating purchasing the LaMotte Alkalinity (kh), Calcium Hardness
(gh),
and Hardness (total). Would I be overdoing it by purchasing all three?
Hardness is sometimes confusing for me. I understand carbonate hardness
(kh)is also called 'alkalinity' and that I add baking soda to increase
the
kh and stablize the ph. I understand that calcium hardeness (gh) is also
called 'general hardness' and I am just now experimenting with raising the
gh with gypsum which does not raise my ph of 7.4. Do I need to know the
total hardness (what symbol is it?) and what do I do with that info? add
something?

What gets confusing is when I look thru my catalogs at the test kits shown
and they show alkalinity (ok), carbonate hardenss (ok), hardness (gh or
kh?) calcium (is this a hardness test or just for reef aquariums?), total
hardness(?). Can anyone decipher the question marks for me?

Thanks,
Barbara