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Thread: help me understand PH, please :-)

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    help me understand PH, please :-)

    Hi,

    I have a little problem that perhaps have some simple explanation.
    According to poolcalculator to lower PH in my (50000l) pool by 0.2 I need to add 200ml (34%) of muratic acid. However in reality I need to add 500ml to get the desired effect. The pool is definitely not twice as big . So what am I doing wrong?
    The label on the acid bottle says: "hydrochloric acid 32-34% w/w".

    how long does it take the acid to dissolve in the pool and affect the PH?
    my PH seems to be climbing up by 0.2 in 10 days. It is normal isn't it?

    cheers
    Pawel
    16000 gallons, SWG, IG/concrete, sand filter, the pool is 20+ years old probably

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    Richard320's Avatar
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    Re: help me understand PH, please :-)

    Doublecheck that you have entered all the numbers properly, especially Total Alkalinity. High TA will cause pH to rise quick, and it also increases the acid needed to affect pH changes.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
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    Re: help me understand PH, please :-)

    Quote Originally Posted by Richard320
    Doublecheck that you have entered all the numbers properly, especially Total Alkalinity. High TA will cause pH to rise quick, and it also increases the acid needed to affect pH changes.
    thanks Richard.
    didn't know that the other settings affect the calculation. Now it tells me I should add 320ml. It is better but it is still way off. I guess I'll measure the pool again (it has really odd shape) to make sure I didn't make any mistakes last time.
    My TA is way to high (150) and I'm waiting for it to drop. 150 is the recommended level here (by pools hops) and I raised it before discovering this forum...

    Pawel
    16000 gallons, SWG, IG/concrete, sand filter, the pool is 20+ years old probably

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    JasonLion's Avatar
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    Re: help me understand PH, please :-)

    Muriatic acid takes up to 30 minutes to mix in with the pump running, often shorter but best wait the half hour to be sure.

    Along with TA, the borate level also has a large impact on the amount of acid you need to use.

    Pools with rapidly rising PH can increase in PH between the time you added acid and the next time you take a measurement. If you are waiting overnight, or longer, the PH probably went lower than you thought and then rose again between the acid addition and the next PH measurement.
    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

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    Re: help me understand PH, please :-)

    I usually add acid in the evening and test the result in the morning. I guess it can raise a bit overnight but the change will be difficult to measure. I use Taylors K-1000 to measure PH. Is there something better/more accurate available?
    16000 gallons, SWG, IG/concrete, sand filter, the pool is 20+ years old probably

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    JasonLion's Avatar
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    Re: help me understand PH, please :-)

    No, the PH test in the K-1000 is the best available (without getting significantly more expensive).
    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

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