I have a ~450 gallon hot tub which I keep sanitized via 3 step bromine method (and ozonator), employing 10% Purox bleach for bromine activation. On average the tub sees 2 adults 2-3 times a week. I find that whenever I add the Purox (to either shock or just bump up sanitizer), I'm then fighting high pH levels. I try to keep pH around 7.5 and I've tried TA levels anywhere from 30 to 120, but (a few hours) after adding my bleach, pH shoots up to 8.2+. I understand this is normal with bromine levels over 10ppm, but even when I'm just adding the bleach to bump up to less than that, my pH raises significantly.
I shocked (to ~15ppm 'FB') 2 days ago, then brought pH down to about 7.6 via 4 tablespoons of dry acid. 'FB' is currently at about 9ppm, pH 7.6ish, and TA is about 80-90. I also have some borates in there from the addition of some Borax months ago, but that's been diluted by water top ups and so fourth. Likely a nominal amount.
So, suggestions anyone? Or is it normal to have to bring pH down after the addition of bleach?