I need to get myself a testkit to measure KH, but even then i dont think
it would be my plants: i have had this problem for a while, and the tank
has been until recently quite poorly planted.
In that case, I would guess that either your water naturally has a high pH, or
there's something wrong with the test kit. (Test kits often give weird results
when they get too old. It's best to buy them from a store that does a lot of
business. That way, you know it hasn't been sitting on a shelf in storeroom
for five years.)
Leigh
http://www.fortunecity.com/lavender/halloween/881/