Dont use Chemicals.
A properly maintained tank should not need any help from Chemicals.
If you are having problems with ammonia, your tank is either not cycled all the way, overstocked or underfilterd/undermaintained.
So proper filtration, weekly water changes and proper stocking levels will take care of any ammonia.
As for PH, unless you have fish like Discus that are sensitive to that sort of thing, PH is really not something you need to mess with.
As long as PH is Consistant and does NOT fluctuate, then your fish will be fine. Most fish can thrive in a range from 6-8. As long as the level stays the same.
Lowering and raising the PH can actually be harmful.