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Thread: pH won't lower

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    pH won't lower

    I am trying to lower my pH but do not seem to be making any progress. Test results as follows:

    FC - 4.0
    CC - 0
    CYA - 40ish
    TA -115-120
    PH - 7.9

    Trying to get the pH down to around 7.6 or so. Per the pool calculator I should add 21 oz. muriatic acid. I have added about 20 oz. so far but it has not seemed to drop at all. Granted it is a color test, so subjective, but I have not really noticed a change in color of the dye test. I am somewhat apprehensive about adding too much acid to the pool so before going further dumping more in, I thought I would get some input. Am I missing something or should I keep going with the acid?

    Thanks,
    Rob
    25K gal vinyl inground, 1HP Hayward Pump, Hayward DE 4820 Filter

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    JasonLion's Avatar
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    Re: pH won't lower

    I get 35 oz, not 21 oz. Did you remember to enter your current TA level when calculating the PH change?

    Another thing to watch out for is lower strength muriatic acid. Some places sell half strength, or various other strengths, instead of the full 31.45% that the Pool Calculator defaults to.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: pH won't lower

    With a TA of 120, using the Pool Calculator, I get 24 oz. of 31.45% HCl- to lower the pH from 7.9 to 7.6.

    Are you also certain about your pool volume in gallons?

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    Re: pH won't lower

    I agree with 257's # of 24 oz. I am using the 31% acid. As stated, I'm at 20 and really am not seeing a change. TA is somewhat on the high side, is that having any affect? As far as the gallons, don't have an exact number but I'm sure I'm within 1,000 gallons.
    25K gal vinyl inground, 1HP Hayward Pump, Hayward DE 4820 Filter

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    JasonLion's Avatar
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    Re: pH won't lower

    I calculated lowering the PH to 7.5, which would be the normally recommended target level, but isn't what you said. And you are right, 20 oz should have been enough to show a visible change in PH.

    The PH could well have gone up since you added the acid. I would add another 20 oz of acid, run the pump for an hour, and test the PH again.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  6. Back To Top    #6
    MyBad's Avatar
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    Re: pH won't lower

    Maybe you have 15% muratic acid, I went to Home Depot and bought a box, just like always. Calculated the amount with pool calculator, added the acid and nothing. So I did it again, and the pH dropped very little....anyway took a look at the box and sure enough it was half the strength they normally have!!?? Didn't even notice when I was buying it.

    MB
    Looking to build a new POOL

  7. Back To Top    #7

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    Re: pH won't lower

    This is actually one reason why I like the acid demand test when it comes to correcting pH. If I can add a drop of acid demand reagent and make the color improve to something I like better, then I just think that it is that much easier to dose it and fix it.

  8. Back To Top    #8

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    Re: pH won't lower

    What is the acid demand test?
    25K gal vinyl inground, 1HP Hayward Pump, Hayward DE 4820 Filter

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    svenpup's Avatar
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    Re: pH won't lower

    It is included in the K-2006 kit (among others). It basically is a measure of how much acid is needed to "move" the pH by a certain amount. Once you measure pH you add drops of the Acid Demand reagent to the pH sample until the color matches your target pH. Then you look up in a table how much acid is needed. There is also a Base Demand you can use if your pH is low.

    I use the pool calculator is lieu of the Acid Demand test, which is accurate enough for me for moderate pH changes.
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