I have used the Interpet tablet test kit which said my water was 8.2 Ph, and my nitrates were always at around 50-70ppm, then I got a Hagen mini master kit (same as the master kit in the briefcase but only has nitrate, nitrite, ammonia, and Ph) and that says my Ph is 7.5, and I had real problems with the nitrate test in that it always said 0-10ppm.
I took a sample to my LFS, and they found my nitrates to be 30ppm. I dunno what to believe!!!!!