Are these rocks likely to be buffering my water?

[jschall]

I want to lower the pH of my water. My tapwater is at like 8.0, tank water is the same. I did a 25% wc with RO water, pH is still 8.0.
Is it my rocks that caused the pH to stay the same? How can I bring the pH down slowly and safely, without staining my water yellow?
Do I just need more RO?