Correct me if I'm wrong, but I think I read somewhere that organic
materials
like wood or peat lower the pH of the water by leaching mild acids into
the
water. This will lower the pH , but it doesn't change the gh / kh . If
these
materials don't absorb minerals , they would actually INCREASE the total
dissolved solids ( TDS ) .

Again , I may be wrong . If so , please explain why ....

Indeed, peat does work by leaching tannins into the water, thus acidifying
the water and also depleting the KH content of the water, making it softer.
Dependent on the type of peat used (I use Irish moss peat), the pH is
dropped from a pH of over 8 to 5.5 and the KH drops from 13 to a respectable
3. The colouring, although not to everyone's liking induces certain fish to
spawn and also brings out a more intense colouration in the fish. I have
also found the tannins to be beneficial in the control of algae.

Regards

Mark
www.marksfish.f9.co.uk