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Thread: Chlorine Concentration

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    Chlorine Concentration

    Am I correct in assuming that now that I lowered my CYA to 40 and now can maintain a FC level of 3-5 instead of 7-12 when my CYA was over 100 that the concentration of chlorine in my pool is 1/2 to 2/3 less meaning clothes, pool floats, etc... wont' bleach out as fast?
    18,500 gallons, Cartridge Filter, In Ground Plaster. Jandy CL460 Filter

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    Richard320's Avatar
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    Re: Chlorine Concentration

    Yes and I don't know.

    Yes, you can maintain a lower FC level and have the same protection you had.
    I don't know if things will not bleach out as fast. The higher FC was bound up to the higher CYA, so you should have the same available chlorine as before. I know that affects the sanitizing, I don't know if it works the same for bleaching.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Re: Chlorine Concentration

    Thanks Richard. I didnt really know if understood it either. I know the reason for the higher FC was due to the higher CYA bonding to the chlorine more but I don't really understand how that affects the bleaching action of swimmers and gear.
    18,500 gallons, Cartridge Filter, In Ground Plaster. Jandy CL460 Filter

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    Ohm_Boy's Avatar
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    Re: Chlorine Concentration

    My understanding* is that the higher FC for higher CYA is to maintain a common effective chlorine (oxidizing/sanitizing) level. This means, to me, that any bleaching effects should be the same. Hopefully, this shouldn't be a problem at normal recommended levels.


    *My understanding can be quite limited, as I AM an idiot.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

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    Re: Chlorine Concentration

    Ohm_Boy, your understanding is right on. The active chlorine (hypochlorous acid) level that is what bleaches swimsuits and oxidizes skin and hair is roughly proportional to the FC/CYA ratio. So 10 ppm FC with 100 ppm CYA is roughly the same as 4 ppm FC with 40 ppm CYA in terms of its effects. The chlorine bound to CYA isn't completely innocuous, but its oxidizing power is 1/100th as strong.
    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
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