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Thread: FC Level While Swimming

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    FC Level While Swimming

    Good Day.

    Last summer we installed a 18X36 in-ground pool and I successfully used the BBB method from day 1. There seems to be some debate about the long-run effects of chlorine exposure so to try to minimize exposure I keep the chlorine level as low as possible when people are in the pool, typically between 0-1ppm. I subsequently raise the chlorine level immediately following usage. In addition, I periodically, when the pool wont be used for a couple days, raise raise FC to burn off CC. In order to accomplish all of this I do not use stabilizer. I am sure I spend more on bleach than I might otherwise but that is a secondary concern.

    I am not here to debate the long-run heath effects of chlorine exposure. What I am curious about is if you guys see any problem with how I manage FC with bathers in the pool? My guess is that bacteria is spread more easily given almost non existent FC but is this really a problem in practice, given relatively clean kids etc...?

    Maybe a half-step would be to increase FC to 3-5ppm when I expect lots of little kids?

    Thank you for your insights,
    J

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    JasonLion's Avatar
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    Re: FC Level While Swimming

    Your approach is more expensive, more work, and more dangerous. Failure to maintain appropriate FC levels can easily lead to many kinds of problems that are drastically more serious than the extremely minor side effects of chlorine.

    For example, keeping CYA at zero causes chlorine reacting to bather waste to produce far more of the dangerous chlorine by products than would be produced if you were using CYA.
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    Re: FC Level While Swimming

    Quote Originally Posted by JasonLion View Post
    For example, keeping CYA at zero causes chlorine reacting to bather waste to produce far more of the dangerous chlorine by products than would be produced if you were using CYA.
    Just the kind of information I was looking for. Could you point me to some information that would help me learn about this process: the interaction between chlorine, cya and organic compounds?

    Thanks so much,
    J

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    Richard320's Avatar
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    Re: FC Level While Swimming

    I think what you want is in here: http://www.troublefreepool.com/threa...ater-Chemistry

    The very first graph shows the Hypochlorite to FC ratio at various CYA levels.
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    JesseWV's Avatar
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    FC Level While Swimming

    I think what the OP needs to realize is that with CYA present, the active amount of hypochlorous acid is LOWER than what he/she is providing even at 0.5ppm.

    0.5 ppm FC @ 0 CYA = 0.255 ppm HOCl (as ppm CL2)

    4.0 ppm FC @ 30 CYA = 0.060 ppm HOCl (as ppm CL2)

    EDIT: Complete CYA/HOCl relationship table HERE.

    Basically you're exposing swimmers to over 4 times the amount of active chlorine, you have no protection from the sun and no reserve FC once it's depleted.

    Cyanuric Acid is a great product which makes managing any pool much easier as long as it's kept within recommended ranges. I think most members of the forum will agree that if there isn't a law forbidding it's use, it should be used for the reasons mentioned here and in countless threads.
    Last edited by JesseWV; 04-24-2014 at 01:01 PM. Reason: Added table link
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    Re: FC Level While Swimming

    Best responses ever.

    Thanks for the help.

    I spent a long time reading the referenced posts and have a much deepering understanding. The pool company added CYA when they filled the pool so the levels were >0 so I think I was safe and did not expose people to higher levels of HOCI through my ignorance. Now I am better prepared and will shoot for 30ppm CYA while continuing to maintain chlorine at the lower end of the suggested range.

    Thanks again for pointing me in the right direction.

    Edit: I have no idea how that signature got there but it is completely wrong.

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    JasonLion's Avatar
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    Re: FC Level While Swimming

    We had some signatures get switched around and duplicated to other people during our software upgrade last winter. Sorry about the confusion.
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