On Sat, 12 May 2007 17:19:26 CST, Joan wrote:

I'm not a chemist, but maybe the sulfate doesn't have the same
buffering capacity as carbonate.

Let me try again. The calcium sulfate (plaster of Paris.) when
dissolving into the water carries calcium carbonate into solution.
Calcium carbonate in limestone stops entering solution when the pH of
the water reaches 7.8. Sorry if I mislead you, but I thought Ingrid
knew that. You are correct in wanting calcium carbonate to buffer KH,
so do I. However calcium can also enter the water and register on a
tester as GH, but I want calcium carbonate in the water and to
register as KH on my test kit.

I'm not a chemist either, just a dummy with soft water and a few
experiences, trying to learn something.

Regards,

Hal