Is your ph changing all the time ? or is it always around the 8 mark.
A ph of 8 is not all that bad, but if it's up and down and all over the place that's not good.
I found this regarding ph levels.
The best way to tell if you water is fish-friendly is to test for PH. In most cases, A steady pH is much more important than a "target" pH. A fluctuating pH can be very detrimental, whereas a fish can get used to a "higher" or "lower" pH with some time. A PH level of 7 or 8 is about the max you would want to see.
Chances are that the fish you buy are from your immediate area....from a fish store is likely to have the same (or similar) water source and have been acclimated to the water already. However, is is very important to follow the acclimation process below.
It is good information to read species profiles on the fish you are going to have to identify target PH values. However, remember these are for fish living in the wild. You will usually be purchasing fish who have been bound and captively bred.
Specific pH comes into play when trying to get certain species to breed (and even then, it can be questionable).
One thing that can be said on this topic is that it is not pH problems that kill fish.