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Thread: Question about CYA and FCC relationship.

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    Join Date
    Jul 2015
    Lake Elsinore, CA

    Question about CYA and FCC relationship.

    How come chlorine / other pool care productions don't mention the CYA FCC relationship? Where can I go to learn more about this relationship?

    Pool a supply stores never mentioned this either?
    Intex 9 x 15 x 52" 5000 gal, vinyl, Sand filter pump, Taylor K-2006

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    TFP Guide

    pabeader's Avatar
    Join Date
    May 2015
    Cartersville Ga

    Re: Question about CYA and FCC relationship.

    Because if they admit it, they would be out of business.

    You can start here:
    Bob - Soon to be INTEX 12x24 owner, 'New to me' Kreepy Krauly Sand Shark, Test kit: TF-100 w/Speed Stir

  3. Back To Top    #3
    Patrick_B's Avatar
    Join Date
    Jun 2011
    Midland TX

    Re: Question about CYA and FCC relationship.

    Many are also unaware, and the FC CYA relationship is just plain misunderstood by many others. Unfortunately, the government, and most industry "authorities" don't recognize it.
    TFP Moderator
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  4. Back To Top    #4

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Question about CYA and FCC relationship.

    It's a chemical fact known since at least 1974 as defined definitively by the equilibrium constants determined in this paper. It was known even before then, but all of the equilibrium constants had not been worked out. The bottom line is that the active chlorine (hypochlorous acid) level that determines the rate of disinfection, killing of algae, and oxidation of bather waste is proportional to the FC/CYA ratio (when CYA is present). So if the CYA rises over time and you don't proportionally raise the FC, then the ratio drops which means that in the presence of sufficient nutrients algae can grow faster than chlorine can kill it.

    It's not just the FC/CYA relationship that the pool/spa industry chooses to ignore, but also the following chemical facts that are independent of concentration of product or of pool size:

    For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
    For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
    For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.
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