Question about PH bounce

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

Judy,
I'd wait a couple days before doing anything about the pH just to be sure the water is mixed up well. Your bouncing could be due to circulation issues, when and where you take the sample, etc.
Al

First--try Poconos's advice. If that doesn't work...

Second -- With a vinyl pool you can safely bring your T/A as high as 180. I'd start by bringing it to 120-130ppm. See if that helps.

Third--you didn't say what your CYA is--if it's very low (like well below 30, or below 20), you can try chlorinating with Di-Chlor powder or Tri-Chlor tablets or powder. Both add CYA, so if it's low they will help and both are VERY acidic, especial Tri-chlor.

Fourth--Do you have a salt water generator? If so they are frequently to blame for rising pH.

Missing one datapoint: what's your alk level?

Michael

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MY TA is 100.

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Michael:

It was toward the bottom of the thread-starting post. My advice was based on that.

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Originally Posted by CarlD

First--try Poconos's advice. If that doesn't work...

Second -- With a vinyl pool you can safely bring your T/A as high as 180. I'd start by bringing it to 120-130ppm. See if that helps.

Third--you didn't say what your CYA is--if it's very low (like well below 30, or below 20), you can try chlorinating with Di-Chlor powder or Tri-Chlor tablets or powder. Both add CYA, so if it's low they will help and both are VERY acidic, especial Tri-chlor.

Fourth--Do you have a salt water generator? If so they are frequently to blame for rising pH.

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CYA level is 40. Just stopped using the trichlor sticks. I have been shocking with cal-hypo, so I haven't needed to add bleach yet (I think bleach raises PH). I was just wondering if cal-hypo is known to have an effect on PH. Strange thing is, we have had probably 3 inches of rain in the last week or so, and I know rain is acidic, yet my PH continues to bump up.

And, no, I don't have a SWG. Didn't know about them until after pool was built, and I don't think I can talk hubby into spending the money right now. I guess I'll be on the bleach bandwagon. I am hoping I can get to where I check my FC everyday, and add bleach every 2 or 3 days; that will be manageable.

EDITED TO ADD: Re: raising the TA: Now that I know that aerating the water lowers TA, I may have another piece of the puzzle. When I first started testing the water, my TA was 80. PB added chemicals (baking soda?) to bump it up to 130. However, we have 5 deck jets, and we run them alot when we are swimming. Maybe I've dropped my TA, and made my PH a little less stable? So maybe I should raise my TA back to 130?

Judy

Cal-hypo is far more likely to raise pH than bleach. Use that instead. The pH of bleach is high, but it's generally 1 gallon's worth against 10,000 or 20,000 gallons, so it's usually not effecting a change.

Aerating doesn't lower T/A--that's been a confusion around the board. But it DOES raise pH under certain conditions that are part of the T/A lowering process and may be contributing to the rising pH.

I would raise T/A and see if it helps.

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Originally Posted by CarlD

Michael:

It was toward the bottom of the thread-starting post. My advice was based on that.

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Whoops, missed that.

Michael