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Thread: pH so low it doesn't want to rise

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    pH so low it doesn't want to rise

    Last week I went to an indoor pool, which was being taken care of by the customer, or at least one of the customer's employees. The pool was a small fiberglass pool with a treadmill in it. It was right on the line between a big hottub and a small pool. About 8'x16'x4'. They had a problem with algae growing on the walls of the pool, so they called me. The filtration system is basically a hot tub setup. A small cartridge filter, and a second pump to run the jets.

    When I tested the chemistry (using test strips) the chemistry was off the charts low, with the exception of hardness. I shocked the pool, and ran the jets to circulate the water. I tested several times to make sure the Chlorine level was high enough. Then I started working on the pH. I added 4 lbs of ph+ (4lb is usually too much for a 20x40), ran the jets, and tested several times in different locations. The pH was still off the charts low. I added more slowly, testing repeatedly in different locations until I finally saw a slight change on the test strip. I let it run for a while testing every few minutes to see if it was changing. It didn't change, so I added more. Eventually I got the pH up to where I wanted it, so I let the jets run, and continued to test periodically, watching for changes. It seemed to finally be stabilized.

    So my questions are:
    What would cause pH to get so low it would take this much pH+ to bring it back in an indoor pool?

    Was I right to assume that I could watch the pH come up as I waited? I realize that doesn't really work in a full size pool.

    How likely is it that the pH would continue to rise once I stopped adding.

    When I added the pH+ the water turned cloudy instantly. Is this an indication that I added too much, or is it likely a result of other conditions such as algae or bacteria dieing, or precipitation of Calcium?
    TreeFiter

    Pool Technician
    Saugerties, NY

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    duraleigh's Avatar
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    Re: pH so low it doesn't want to rise

    When I tested the chemistry (using test strips) the chemistry was off the charts low, with the exception of hardness.
    One of the first things this forum teaches is never trust test strips. Your readings may or may not have been correct but to assume test strips produce dependable results can really bite you.

    First thing I would do is retest the water using a phenol red drops based pH test. Then we'll all know that the results are trustworthy.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    JasonLion's Avatar
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    Re: pH so low it doesn't want to rise

    The use of trichlor tablets is a common cause of exceedingly low PH.

    In a spa with the jets running the PH tends to come up fairly quickly, fast enough that sitting there and waiting makes sense. In that kind of environment the most common approach is to add baking soda to raise the TA and then run the jets to bring the PH up. The PH will continue to come up every time the jets are run if the TA is too high. With very low TA the PH will often stabilize at low to reasonable levels even if the jets are run.

    Having the water turn cloudy instantly when you add PH+ is almost always calcium clouding. PH can occasionally affect algae and bacteria, but a PH change would have to be followed by at least a few hours while the algae/bacteria grew before you would see any clouding.
    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 so low it doesn't want to rise

    If your pH is really low I would check your alkalinity. Ph will go up naturally if you Alk is high and your water is aerated.

    Ph+ is probably an alkalinity supplement. The cloudiness is more than likely precipitation ask the localized ph spike encourages precipitation. From the aquarium hobby I've learned these things should be added very slowly. Something else you can do is add baking soda vs. soda ash. They are the same thing except that soda ash has been baked and the CO2 driven off. When dosing with baking soda the CO2 will temporarily lower pH however the net result is a higher alkalinity. The pH will go up after the CO2 has left the water surface.

    I'm not a pool expert yet, but I have a very good understanding of the chemistry behind this from keeping saltwater aquariums. I hope this helps...
    ~10-12K gallons, IG, Cartridge, Saltwater, gunite, attached spa.

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    Richard320's Avatar
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    Re: pH so low it doesn't want to rise

    pH results are iffy when FC is really high.

    I would imagine even moreso with strips rather than drops.

    You say you're shocking it?
    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: pH so low it doesn't want to rise

    In an indoor pool there could be CO2 build up inside the building keeping the pH low. This is commonly a problem with fish tanks in the summer and winter months when homes are closed up. It isn't until windows are open and fresh air comes in that the pH rises.
    ~10-12K gallons, IG, Cartridge, Saltwater, gunite, attached spa.

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