moderator note: Split from here:. Constantly rising pH.
I am having a similar problem with a fresh fill on my spa. The fill water was highly alkaline (TA > 250) to begin. I aerated and used MA over several iterations to get the TA down to 50-80, however the pH always settles out at 8.0 - always. If I add acid to lower my pH to the mid 7's, the water bounces back in 2 or 3 hours and settles out at 8.0 again. I recently refilled this tub because I ended up in an endless battle (and lost) between driving pH downward and keeping any kind of alkalinity in the water and eventually drove my TDS through the roof (I use diluted MA now instead of dry for this reason). The water is crystal clear and otherwise enjoyable. I've even switched over to Br as a sanitizer since it has a wider pH spectrum than Cl but I'm concerned about the long term effects on my spa water with its pH perpetually pegged at 8. The local pool guy is stumped and has no explanation. It's almost as if another buffering agent is present in the water that isn't carbonate based.
I've heard some people report success with borates. Am I a borate candidate? If I'm not experiencing scaling or cloudiness, are there any long term ills I risk with just sticking with a bromine sanitized spa at 8.0?
Also of note: my fill water is "softened" well-water (which may explain why my fill TA is so high by CH was next to nil).
Thanks in advance for any advice!