Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
It's possible your water really is very hard.
It's also possible you have an expired test kit. Of the tests I've used, the API GH/KH is the most likely to fail if past the expiration date, and it always fails by requiring an excessive amount of drops to change color. So check that date.
Many fish stores offer free testing of critical water parameters if you bring in a sample. While GH/KH may not be on the normal list of parameters, I think many employees would be willing to open a fresh GH/KH test in store if they don't have one already set aside, then perform the tests for you, if asked nicely. (And if they have no further need of the kit, but you do, you could purchase the freshly opened kit.)
Write down the result. In the future if you retest, and the numbers are much higher by comparison, then you have possible reason to doubt the test.