Lots of fish acclimate to a fair range of pH even higher than 7.6.
However, you said your test kit went up to 7.6. It is possible that your pH could be much higher and the kit just doesn't show it.
If you are worried about pH, you can take a sample to the
LFS and ask them to do a high-range pH test. My high range kit tests 7.4 to 8.8. I rarely use it since I inject
CO2, so I'm watching a 6.8-7.0 range.
Again, though, if your pH is rising slowly, the fish may adapt just fine. Unless you are keeping fish that are very picky about the pH, I would look to other reasons.
If your pH is constantly swinging, that would be more of an issue. Often it is not so much a matter of having "proper" numbers - it is all about having consistant numbers.
By the way, my Q tank has no
CO2 injection, and our water is at least 7.5 if not closer to 8. My fish (Green Terror, Tiger Barbs) are fine with that. The
LFS has a similar pH range, so I only have to worry about pH acclimation when I bring fish into my lower-pH
CO2 tank.