The Aquarium Pharmaceutical kits are good ones. How long have you had the kit - how old is it? They don't have expiration dates but I write the date that I buy it on the box, and when it's about a year old, I buy a new one.
I don't think your distilled water pH is off, though. I mix tap and RO
water for my tank (my pH out of the tap is 8.2) and my RO
pH is 6.2 or 6.4. I always thought that RO
water and distilled water are neutral too, but my RO
water is always on the acidic side.
When are you testing your tap water pH? Like Fishyfanatic says, you should test the water after it's been sitting out, at least overnight. This is called "aging". After aging, my tap water pH is 7.8 (it was 8.2 out of the tap).
Your tap water seems similar to mine. I'm wondering if you mixed up your KH
values. My KH
(of tap water) is 3, and my GH
is 9. I also noticed that your tank has a nitrite reading of .25. Is the tank cycled? Double-check the reading again and do an extra water change this week if you're still showing nitrites.