You need to dial in your alkalinity first. Actually...how I balance my tub is this.....I get the calcium hardness in check(I keep mine at 210-230 ppm). I then balance ALK(100-120 ppm). Then I balance ph (7.4-7.6). Lastly,I add the sanitizer(I use Di-chlor).
Balance your chems in moderation,and do it gingerly over several days. After you've done it a few times,you will get a knack/feel for it.
GL