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Thread: FC/CYA safe levels

  1. Back To Top    #1

    Join Date
    Oct 2008
    Location
    Terre Haute, IN
    Posts
    51

    FC/CYA safe levels

    I have read a few threads that all support that higher FC levels are okay and safe at higher CYA levels for proper sanitation. Using the Best Guess CYA chart I see the Min/max and shock levels. Is the max FC the same as the threshold needed for safe swiming again after a shock? Is there a chart somewhere that suggests the level where its okay to swim again if your runnning with a higher CYA's??? I know suggested levels most people say 5-10FC (i've seen debated threads over this value).

    But does it take a long time with a CYA of 100 and taking it to 25ppm for a shock for it to come back down?? Could it mean days with no swimming? Live in midwest don't have the intense sun like the folks online here TX and FL areas.

    Curious to know because before BBB I got my CYA up high by accident and plan to run with it for a while but need to know what I'm getting into should I need to give the pool a shot of 25ppm FC.

  2. Back To Top    #2

    Join Date
    Aug 2008
    Location
    Collierville, TN
    Posts
    108

    Re: FC/CYA safe levels

    Just want to chime in here and let you know that it seems like you and I are in similar situations with the high CYA. I'm looking at quite possibly a reading as high as 300
    Pam
    approx. 30000 gallon IG 40x20 vinyl pool w/ cartridge filter

  3. Back To Top    #3
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,887

    Re: FC/CYA safe levels

    Yes, higher FC levels are safe at higher CYA levels. CYA "deactivates" some of the chorine, the more CYA the higher the percentage of chlorine that is locked up with the CYA. Because of that the active disinfecting chlorine level remains more or less the same when you follow the FC/CYA relationship outlined in this chart.

    My personal rule of thumb is that anything below shock level for your CYA level and at or above the minimum level is safe. There is solid evidence to suggests that levels noticeably higher than that are also safe, but I like to be conservative.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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