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Thread: Using dry ice to lower ph

  1. Back To Top    #1

    Join Date
    Jul 2009

    Using dry ice to lower ph

    I’ve found a nearly free, if erratic source for dry ice and remembered this post: which tells me that one pound would drop my ph from 7.5 to about 7.25 which I have confirmed.

    I want to use dry ice in lieu of muriatic acid when I can, does anyone have any hints or tips? Can I just throw it on the plaster in the deep end or will the cold damage it over time? I’ve already done it three times with no noticeable damage, but hate expensive surpises.

    I’m considering fastening to cheap colanders together to create a sort of giant “tea ball” to keep it off of the plaster and shrink the bubbles down to increase the absorption of the CO2…
    20,000 Gallon kidney sort of a sand filtered gunite in ground pool w/ hot tub.

  2. Back To Top    #2

    Re: Using dry ice to lower ph

    I think that the effect would be only temporary as the co2 that turns to carbonic acid would eventually outgas over a few hours- just a guess though
    14'x28' vinyl liner inground 3.5-6' deep wedge hopper 15000 gal (used to say 13000- I calculated wrong), 1 hp pump with sand filter, 2 returns, 1 fountain, traditional chlorinated, pool house.

  3. Back To Top    #3

    Join Date
    Dec 2009
    Central Massachusetts

    Re: Using dry ice to lower ph

    Plus I would think your TA would increase as well.
    Muriatic acid is pretty cheap.
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

  4. Back To Top    #4

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Using dry ice to lower ph

    Quote Originally Posted by bk406
    Plus I would think your TA would increase as well.
    The TA remains unchanged. It is the exact opposite of carbon dioxide outgassing. When adding carbon dioxide to the pool, such as with dry ice, the pH drops with no change in TA.

    If one is lowering the pH that has risen from carbon dioxide outgassing, then it is the perfect see-saw with no change in TA. In practice, there will be a rise in TA over time from using chlorinating liquid or bleach from the excess lye and that will need acid to get the TA lowered again. The perfectly balanced situation would use enough acid to compensate for the excess lye in bleach and enough dry ice to compensate for the outgassing of carbon dioxide. Of course, one could just lower the TA level and have less of a pH rise in the first place.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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