I've had my pool for about 14 months. For the first year+, the pH would climb roughly 0.1 per day. So, I would add a little acid every couple/few days to keep it in check. From what I gather, this is normal for a newish plaster pool.
But for the past week or so, though, the pH has been climbing at twice that rate--about 0.2 per day. I have no idea why this is.
I'm measuring pH with a Taylor kit, and with a pH meter I bought a few weeks ago. The two of them always agree on the pH reading.
Everything is pretty much within spec:
FC: 9 ppm (a bit high, I know)
CC: 0 ppm
TA: 60 ppm
Calcium hardness: 350 ppm
CYA: 60 ppm
Salt: 3,000 ppm
Borates: 50 ppm
I added boric acid a month ago. It didn't do anything much to the pH at the time, nor for at least the 3 weeks after.
I haven't been doing anything different lately, other than adding ~6 ounces of Jack's Magic "The Magenta Stuff" every weekend for the past 3 weeks.
Nothing else unusual is going on, that I can tell. The water looks great. Nice and clear, no stains, etc. What could account for the doubling of the pH change rate?
Aaaaand... I just realized I've been running the pool's two arcs ("waterfalls"), which can increase pH. I can turn them off for awhile to see if that makes a difference. BUT... I've been running the arcs for several weeks! So, I am still confused!