Originally Posted by Nemo the Clownfish
Nobody wants to hear this but people advise not to fight with the water, but accomodate your stock to what does well with your water parameters. You can look in the fish and plant listing for what tolerates pH 7.6 - I think maybe livebearers could be the place to start.
You can expect the pH to slowly drop over time as the tank "breathes" and ages
I hear this alot too as far as don't fight the water. True that it is easier to keep fish suited for tap vs making tap suitable for the fish. With this approach,your fish selection is limited. Fish are adaptable fortunately and can be acclimated to most water parameters within reason. The way I look at it, if there is a group of fish I want to keep, I will do everything I possibly can, to provide suitable parameters instead of settling for fish I don't really want to keep. For instance cardinal tetras and cichlids will require two totally different parameters. My tap suits cichlids better but that is not my intent to keep them.
I'd avoid using chemicals if at all possible. They are less stable and require alot of trial and error vs using natural elements. CO2 and R/O water are two options that can lower ph without chemicals. The only problem with distilled is the expense. Distilled water is pretty close to RO water if not the same. RO units can be a bit pricey but they will pay for themselves in due time. As far as the ratio, you will have to experiment to see what works for you. I use 60/40 to 70/30 with my tanks that house cardinals.