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Thread: PH/TA Acid/Baking Soda And Round and Round We Go!

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    PH/TA Acid/Baking Soda And Round and Round We Go!

    Scenario: My TA is on th low end at 60 and my Ph is 7.8. I add acid to lower my Ph and in so doing I lower TA below 60. I then add Baking Soda to raise the TA which in turn raises Ph which in turn causes me to add acid to lower Ph and thereby lower TA. Doesn't this become a circular??
    Steve
    Atlanta, GA

    Inground Vinyl, 30,000 gallon, 20x40 Lagoon, Pentair Single Speed 1-1/2 hp Superflow, Pentair SD 80 Sand Filter, Polaris 280 cleaner w/ Booster pump, Pentair Easytouch.

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    Mod Squad JohnT's Avatar
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    Re: PH/TA Acid/Baking Soda And Round and Round We Go!

    Adding acid only lowers the TA temporarily unless you aerate the pool.
    TFP Moderator
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    Re: PH/TA Acid/Baking Soda And Round and Round We Go!

    John, are you refering to TA or did you mean Ph? Thanks.
    Steve
    Atlanta, GA

    Inground Vinyl, 30,000 gallon, 20x40 Lagoon, Pentair Single Speed 1-1/2 hp Superflow, Pentair SD 80 Sand Filter, Polaris 280 cleaner w/ Booster pump, Pentair Easytouch.

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    Re: PH/TA Acid/Baking Soda And Round and Round We Go!

    If you add acid, that lowers both the pH and the TA. Baking soda should mostly just increase the TA. If you find that the pH is also rising, then that would have happened anyway from outgassing. If you add enough acid to lower the pH to 7.5, then the TA only drops by around 3 ppm unless you have 50 ppm Borates in which case it drops around 7 ppm. If you then add a small amount of baking soda to raise the TA, say by 7 ppm, then the pH barely rises from 7.5 to 7.52. I suspect you are not seeing a true drop in TA as large as you think, possibly due to measurement rounding, so you are adding too much baking soda. Either that or what you are adding is really a pH Up product instead (i.e. sodium carbonate instead of sodium bicarbonate).

    Since the TA shouldn't be that low after the acid addition -- probably measuring at 50 ppm -- just see what happens. The pH may still slowly rise, but probably not quite as fast. If you do operate your TA that low, then you may need to raise your Calcium Hardness (CH) or your pH target. That is, you can settle on 7.7 as your target and not try to fight to maintain 7.5. Your SWG is the primary source of pH rise. Some of this is from aeration for more carbon dioxide outgassing, but some seems to possibly be from chlorine outgassing since the TA won't have any effect on the latter. Do you have a short pipe run from your IC40 SWG to the returns in your pool? If so, try pointing them somewhat downward. That might help with pH stability, though would hurt surface circulation to the skimmer.

    If you have not done so already, you could consider adding 50 ppm Borates to your pool as described here.

    Richard
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: PH/TA Acid/Baking Soda And Round and Round We Go!

    That answers my question Richard. The slight affect on Ph from the baking soda is the piece that I was missing in my mind. I have my borates at about 30ppm now. Would you recommend closer to 50ppm for borates?
    Steve
    Atlanta, GA

    Inground Vinyl, 30,000 gallon, 20x40 Lagoon, Pentair Single Speed 1-1/2 hp Superflow, Pentair SD 80 Sand Filter, Polaris 280 cleaner w/ Booster pump, Pentair Easytouch.

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    JasonLion's Avatar
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    Re: PH/TA Acid/Baking Soda And Round and Round We Go!

    Borate is typically kept between 30 and 50. Since borate will tend to go down over the course of the season, from splash out, backwashing, etc, it is common to raise the borate level to around 50 and then allow it to drift down to 30 over the course of one or more seasons.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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