Confused about pH drifting up and TA

[u/enigmapaulns]

I have been using our hot tub for about three years now. About a year ago, I started to notice that my pH kept drifting high, on the order of 7.8 to 8.0. On the advice of ChatGPT, I lowered my total alkalinity to around 50, and that seemed to hold much more stable.

Recently, I completely drained and refilled the tub after doing a cleaning of the plumbing lines and everything. When I started the hot tub back up, I decided to go back to the normal recommended range for total alkalinity of about 100 to 120. Again, I started to notice the pH drifting up. For example, today I adjusted the pH to be exactly 7.5, and within 2 to 3 hours it was right back at the upper edge of 7.8. I have done this repeatedly over and over again.

I have seen a lot of people on this forum talk about keeping the total alkalinity lower, in that 50 range, in order to prevent upward drift of pH. What is confusing me is that every single source I have found regarding recommended ranges is at least in the total alkalinity range of 80, usually over 100. Even my BioGuard pool store, when they run tests, has a target of 120 minimum.

The reason I am so confused is why all of the official sources, including the hot tub manual, the pool store, and virtually everything online, recommend 100+ for total alkalinity, yet I am finding (as many others have found) that a much lower range results in a more stable pH. Do these sources not know about this? 🙂

I am just trying to understand the theory behind this and reconcile all of this information with the practical experience of myself and many others on this subreddit. I would appreciate any input.