I have an issue with my pH constantly rising and I alway have had this issue. My TA is a little high, at 100, but no big deal. I have maintained the pool well over the past several years and I regularly pour in 1/2 gallon 1-2 times per week. The SWG is constantly bubbling and I believe it is the greatest source of aeration because recently, when I SLAMmed my pool (due to some green algae issues) and turned off the SWG, pH before and after the shock were fairly similar over several days. After I turned the SWG back on, the pH started increasing as usual.
I also have very high CH--about 750. We are perpetually in a drought and our fill water is pretty hard too so I only drain the pool in the winter when we get rain. We didn't get much rain this winter. I have run my pool with high CH for years and simply try to keep the pH <7.8. What I do have (and always have had) are what look to be Calcium flakes that settle to the bottom of my spa. I always keep a little pool water returning to my spa (I have a manual bypass that I use for that). The returns in the spa are near the floor and the spillover is on the opposite side and (of course) at the top of the spa. Thus, my spa is basically a settling tank where only the "scum" gets removed regularly but stuff that is in suspension will settle out to the bottom over time, forming "sludge." (I did some work years ago designing wastewater treatment plants and those really are the technical terms.)
The Calcium flakes are no big deal but I dislike that when I get in the spa, they get suspended and make the water turn cloudy. To mitigate this, every now and then, I manual drain the spa into the body of the pool using the controls at the Jandy control center and let it refill with nice clear pool water. I also vacuum them carefully with a manual spa wand. I wish I could drain the spa to waste but I have a cartridge filter so I don't have a valve for that.
To make things worse, my variable speed driver on my Ikeric filter pump is broken and doesn't turn the pump on consistently, so I have the pump (and SWG) running 24 hours, most of that time on a VERY low speed to save energy. My FC is 7 and my pool is very clear because I have a main drain and a suction-side PoolCleaner that sucks up any flakes that settle in my pool. Keeping the FC on the high side because I get a lot of sun and am expecting a large bather load with 2 parties coming up in the next 2 weeks.
Today it occurred to me that I might want to test the pH of the spa water to see how different it is from the pool water. I had just added acid and the pool water was about 7.1. The spa was 7.4. This was after letting the acid mix in for an hour.
Why is the pH in the two vessels so different? Aren't they one body since I have the spillover trickling all the time? I think I know the answers but I'd love to see if my theories pass the smell test with some of you:
Maybe it takes longer for the pH to change in the spa after an acid addition? Should I add some directly to the spa when I add to the pool? Is the pH always higher in the spa because the water is a little bit warmer (pool around 85 degrees and spa around 93 degrees)?