Something that helped me get a handle on pH swings was keeping a bit of extra attention on how I top off the water. I used to just run the hose straight in, but I noticed my source water had a slightly high pH, which was throwing things off little by little. Now I fill a clean bucket first, check it quickly, and adjust that before adding it to the tub, sounds like extra work but it saves me from chasing pH later.
I also try not to make more than one chemical change at a time. If I tweak alkalinity, I’ll wait until the next day before touching the pH, just to see where it actually settles. Doing both at once always had me overshooting in one direction or the other.
And this might just be coincidence, but since I started cleaning the filters more often, my pH seems to drift less, maybe because there’s less residue feeding the imbalance. Either way, it’s made the whole routine a lot easier.