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Thread: Can't lower pH

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    Join Date
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    Can't lower pH

    FC - 7.0
    pH - 7.8
    TA - 120
    CYA- 50
    Borate - 50


    My TA was down around 60, so I added 8 lb of baking soda, yesterday.
    I waited 3 or 4 hours and it read 130.
    My pH was up around 8.0 so I added 1 qt +3 oz. of muriatic acid. That was 1/2 of what the pool calculator gave to lower pH to 7.2.
    Checked it about an hour later. pH read 7.7 (Guessing at colors), so I added the other quart of acid.
    That was about 2 hours before I turned the pump off.

    I ran it about an hour this morning and pH still reads 7.7 or 7.8.

    I hate to keep pouring acid into what looks like illogical readings. Should I hit it with another quart or wait awhile and check it?

    Thanks
    10,000 gal / Plaster / Cartridge Filter / 1 1/2 HP pump motor/ TF-100 test kit.

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    Mod Squad tim5055's Avatar
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    Re: Can't lower pH

    What test kit are you using? You can add that to your signature so we are sure when we answer.

    Could your FC actually be above 10 and you are getting false high pH? Is there a lot of kids splashing around or a fountain or other water feature running?

    The baking soda would push up the pH a little, and now your TA is a little higher than it should be.

    For your pool you want:
    with Bleach
    FC 3-7 (See chart)
    pH 7.5-7.8
    TA 70-90+
    CH 250-350
    CYA 30-50
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

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    Re: Can't lower pH

    TF-100
    There is nothing going on with the pool- no one in it- no aeration.

    I'll retest the FC.
    10,000 gal / Plaster / Cartridge Filter / 1 1/2 HP pump motor/ TF-100 test kit.

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    BoDarville's Avatar
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    Re: Can't lower pH

    The pH scale is logarithmic, not linear. Each one full point change (e.g., 7.0 to 8.0) on the pH scale equates to a 10X change in the acidity/basicity. In other words, if pH is sitting at 8 and you are targeting a pH of 7.6, you cannot assume that adding half the amount of MA needed for a pH of 7.2 will result in a pH of 7.6. The PoolMath tool accounts for this logarithmic scale.

    In addition, as you add muriatic acid (MA) to lower pH, the TA will also drop. This means that you will need to add less MA to reach your target pH with each subsequent addition. Since MA affects two parameters (pH and TA), you will need to retest both of these before adding MA. Enter your test results in PoolMath to get the proper dosage.

    Another thought...When dosing FC to reach a target, does the dosage stated by PoolMath enable you to hit your target? If not, then your pool volume may differ from what you think it is. If this is the case, it would impact other dosage amounts.
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    JasonLion's Avatar
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    Re: Can't lower pH

    How old is your plaster? Fresh plaster will raise the PH rapidly for the first month or so.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Can't lower pH

    Quote Originally Posted by tim5055 View Post
    What test kit are you using? You can add that to your signature so we are sure when we answer.

    Could your FC actually be above 10 and you are getting false high pH? Is there a lot of kids splashing around or a fountain or other water feature running?

    The baking soda would push up the pH a little, and now your TA is a little higher than it should be.

    For your pool you want:
    with Bleach
    FC 3-7 (See chart)
    pH 7.5-7.8
    TA 70-90+
    CH 250-350
    CYA 30-50
    FC is 4-8 for 50 CYA per the pool calc.

    - - - Updated - - -

    Quote Originally Posted by JasonLion View Post
    How old is your plaster? Fresh plaster will raise the PH rapidly for the first month or so.
    Plaster is 17 years old.
    I readjusted my return jets yesterday and just noticed that 2 of them are causing slight ripples in the water. I don't think it's enough to cause what I'm experiencing but I will readjust them
    10,000 gal / Plaster / Cartridge Filter / 1 1/2 HP pump motor/ TF-100 test kit.

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