I have well water, which is run threw a softening system, arsenic is higher levels so I have to use the water for my tanks, and not just use straight well. I safely lowered my PH, and hardness by mixing it with R/O water to get the "perfect" mix for my cherry red shrimp. Now I have a 5 gallon bucket marked with the exact amount of each I have for water changes and top offs.
And is just your PH high? my KH is around 10-12 which made any attempts at PH lowering additives useless. PH would drop, then 3 hours later it would be back up again.
I wanted to get Crystal reds at one point, But having read that they like PH as low as 5.5 for breeding I decided on the hardier Cherry reds. I'm Very interested in seeing how your project works out. And I hope it works out well!