High PH - Spa spillover raising PH in SW Pools?

[chem geek]

Lowering the TA is ultimately through adding acid, though the process is accelerated by aeration (which you already have from the spillover) and having the pH be lower during the process, but in your case what is strange is that you are adding LOTS of acid but not having the TA drop. I simply do not understand this. Since you've got a lot of pH rise and you add acid frequently, your TA should be dropping. If you had new plaster or a recent replaster, then this would make sense since plaster curing increases pH, TA and CH, but you never mentioned anything about any sort of new or replaster job.

There can be some pH rise from undissolved chlorine gas outgassing and that will also raise the pH, but to have the TA be stable when adding half a gallon of full-strength Muriatic Acid every week, that would require almost 14 ppm FC to completely outgas as chlorine gas from the pool which seems inconceivable.

[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?