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Thread: speed at which pH changes.

  1. Back To Top    #1

    Join Date
    Mar 2009
    Charlotte, NC

    speed at which pH changes.

    The pH scale is a factor of 10 for each number I believe.
    Does this necessarily translate into a difference in time at which the pH can change, or not necessarily because in a pool we also have borates, TA, etc.

    Example; my pH rises steadily from 7.5 to 7.8 about each 7-10 days, so I test it about every 7th day +/-.
    I have an issue going on (raised-stains-stained-bumps-t21024.html ) where I’m keeping the pH at 7-7.2 for a week or so. Is it true that to keep it in that lower range, I should test it more frequently compared to when I am testing to see it go from 7.5-7.8, because it more quickly can go from 7 to 7.3 than it can from 7.5 to 7.8?

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  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: speed at which pH changes.

    That whole line of reasoning is incorrect. If you are trying to keep the PH down around 7.0 to 7.3 you will need to check it more often, but that has nothing to do with the PH scale being exponential. In this case, it has to do with the distance you are from CO2 equilibrium with the atmosphere, lower PH makes you more out of balance, so the rate of change is faster.
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  3. Back To Top    #3

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: speed at which pH changes.

    This chart shows the factor of how much more carbon dioxide there is in pool water compared to what there would be in equilibrium with the air. That is, it shows how over-carbonated pools are at various pH and TA levels. The rate of pH change, however, is more complicated than this since the rate of carbon dioxide outgassing seems to vary as the square of the TA (not more linearly as shown in the table) and the pH buffering changes as a function of pH. Nevertheless, we do generally see the rate of pH rise slow down as the pH gets higher and that is what is predicted by the table.
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