First off: vinyl IG 18' x 40', about one month old.

My PB mentioned something about PH bounce, but I was under the impression that once my TA was where I wanted it, the PH would be somewhat stable. About a week ago, my PH was over 8, so I added dry acid. Had no real effect. Then bought muriatic acid, and added a little too much. Tested again about 6 hours later and it was around 7. Next day (12 hours later) tested, and it bounced back up to 7.8. I have added cal-hypo a couple of times to bring my FC levels up above 15, to try to get rid of mustard algae.

Long story short, I've been adding muriatic acid (now a cup at a time), and testing again a few hours later, and my PH is bouncing each day from 7.8 or above, down to 7.2 or below. I know that I need my PH to not be too high for the chlorine to be most effective. MY TA is 100. Is this much bounce normal? Maybe I shouldn't add muriatic acid every time I get a high reading, but wait 12 or 24 hours and test again? Could the cal-hypo be pushing up my PH?

Thanks,
Judy