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Thread: seems like a ph of 7.2 would be ideal?

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    seems like a ph of 7.2 would be ideal?

    this 1st statement comes from "professional pool operators of America" 12 most common myths of pool water chemistry,

    5. The ideal pH for any pool water is 7.4.
    Impossible to know. Out of context, there is no “ideal” anything. The water’s hardness and other CSI variables, even the values read from the make-up (fill) water, help you determine the most appropriate value. In general, the best pH is “the lowest pH you can get away with” as chlorine works much better at lower pH values. That actual number is, of course, clearly limited by the bottom of the state health-code ranges, and otherwise chosen by pool operators considering the influences and trends of their sanitizer and their make-up water – wisely keeping that CSI thing in balance all along. Curiously, a pH of 7.4 is not even legal in South Dakota where pH 7.6 is dictated, and almost never used in Germany (the birthplace of water-chemistry science) where their national code’s working range is 6.5 to 7.3! Typically, they hold 7.0 or 6.9.

    and this chart is from "Blue science"

    Chlorine Effectiveness Scale as Depending on pH (Potential Hydrogen):
    Active Chlorine------ pH
    97% -------------------- 6.0
    91%--------------------- 6.5
    76%-------------------- 7.0
    66%-------------------- 7.2
    50%-------------------- 7.5
    33%-------------------- 7.8
    17%-------------------- 7.9
    10%-------------------- 8.0

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    Patrick_B's Avatar
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    Re: seems like a ph of 7.2 would be ideal?

    I moved this post here, as it is beyond the scope of the Just getting started forum, where residential owners are trying to learn the basics of every day care.


    Not knowing for sure, and not delving into this, I don't think that information takes the presence of Cya into account. Having it in the water opens up the effective range of FC in different pH levels.
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    JasonLion's Avatar
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    Re: seems like a ph of 7.2 would be ideal?

    That chart changes radically as soon as CYA is present, see the charts in this post. With CYA the effect you describe is drastically smaller, and it effectively doesn't matter what the PH is.
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    Re: seems like a ph of 7.2 would be ideal?

    If you want to know more factual information about pool water chemistry, then I suggest you look at Certified Pool Operator (CPO) training -- What is not taught and the thread Pool Water Chemistry where the post Jason linked to resides.

    The main reason that Germany has lower pH is that they use the DIN 19643 standard which has no CYA in the water and most importantly uses flocculation using alum or iron salts and these require a lower pH to operate effectively. Note that the FC level with no CYA is 0.3 to 0.6 ppm with no ozone or 0.2 to 0.5 ppm FC with ozone (in the circulation path, not the bulk pool water). Maintaining 0.2 ppm FC in a large swimming pool can be quite difficult. This is why we recommend using CYA in the pool as a hypochlorous acid buffer. One can then tune the active chlorine (hypochlorous acid) level to what is needed for adequate disinfection and also to prevent algae growth. You can see a list of kill times for pathogens when the FC is around 10% of the CYA level in this post.

    If you have more technical questions, please post them in this "The Deep End" forum so as not to confuse our regular forum members who generally are not interested in the technical details.
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    Re: seems like a ph of 7.2 would be ideal?

    Yes, I sent a quick PM back to Brushpup that I did not mind it being moved here, also telling him more about my post.

    Did not want my post to seem to be a controversial statement, or such about TFP writings. I love what I have read here, being a new pool owner for the 1st time in my life. Read so much already it really is hard to remember some it, as in numbers. You guys do a heck of a job here, thanks.

    But it does interest me the way some of the chems., interact with each other, (help each other-to what degree), and I am always interested to hear why someone thinks this is the best way to go, and someone else has a slight difference of opinion.

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