blurryblues

I currently have a high GH and low Ph. Source was identified to be my tap water. Although the GH is much higher in the aquarium (lava rocks are the only thing I can think of, contributing to it). KH was 0 and I tried wonder shells and the KH went up but did not alter the Ph. I was considering crushed coral but won't that increase the GH even more? What's the most effective method of raising the Ph without further increasing GH (or even reducing GH)?