High PH - Spa spillover raising PH in SW Pools?

[waterbear]

Sandstone can be formed from either a silica or calcium carbonate (limestone) matrix with either silica or feldspar particles. The second type (limestone) can potentially raise pH and is soluble in acidic solutions.

[jaimslaw]

RE: Sanstone raising PH (or being a contributing factor): I took the test tube, filled it with pool water when the PH was in normal limits, and added some sandstone particles that I scraped of the sandstone facing. I shook it up and then tested the PH - not really too much difference; but I left it in the tube for a few hours and came back to test it, and found a significant increase in the PH. Not saying this explains everything but am still thinking that I have a combination of factors creating this situation, especially that dual spill over spa.

Still hoping someone reading this with a SWG and a dual spill over spa can weigh as to whether any PH problems they may or may not have. Anyone out their with this set up?