"NetMax" wrote in message
. ..

I don't know the mechanism at work when water is softened by boiling, so
the effect may not be permanent, or perhaps it changes state so it does
not register with the test kit and perhaps the fish (?).

As far as I know, boiling causes the bicarbonates in the water to
precipitate out. This releases CO2 and binds some of the kations,
such as Mg and Ca. Since a GH test measures kations, GH drops.
And because CO2 is driven out, pH rises, and KH drops. If you
run CO2 through the boiled water, the previous balance quickly
re-establishes itself.

Cheers,

Michi.

--
Michi Henning Ph: +61 4 1118-2700
ZeroC, Inc. http://www.zeroc.com