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Thread: Using change in FC level to measure pool size

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    Using change in FC level to measure pool size

    I am helping a friend set himself up for self pool maintenance. Ran the tests on his pool last night.

    FC 3.5
    CC 0.5
    CYA 90

    He has an odd sized pool. Our initial estimate of pool size was 15K gallons, and we added in 3 gallons of Chlorox. FC was 21.5 after 2 hours indicating we overestimated the pool size.

    Can I use the change in FC levels to estimate his pool size (should be ~10K gallons based on the change in FC assuming no algae given low CC levels)?

    The test was done in the evening so little Chlorine should be lost to the sun. The only piece I am not sure how to incorporate is the high CYA.

    15K gal, IG, Pentair WhisperFlo, Cartridge Filter

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    Mod Squad tim5055's Avatar
    Join Date
    May 2014
    Franklin, NC

    Re: Using change in FC level to measure pool size

    Yes. While it may take multiple applications of different chemicals to get a more percise volume that way it can be a good way to verify the size.

    I also have an odd shaped pool and narrowed my size down as best as possible that way watching what specific additions of chlorine and muratic acid did to my FC and pH.
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    Join Date
    Sep 2014
    Bakersfield, CA

    Re: Using change in FC level to measure pool size

    I found PoolMath generated additions of mutriatic acid to be very accurate for my pool size before I added borates. Not quite so accurate after I added 50 ppm borates.
    Cheers, Peter
    20,000 gal, 52'x17' kidney shaped IG, Pebble Tec, IntelliPro P6E6VS4H-209L pump. Intellichlor IC40 SWG.
    300 sf Sta-Rite System 3 cartridge filter. Poolvergnuegen 4-wheel suction pool cleaner. TF-100 test kit.

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    chiefwej's Avatar
    Join Date
    Jun 2011

    Re: Using change in FC level to measure pool size

    Use PoolMath. Put in whatever you think for capacity. As you add chemicals and see if it reacts as predicted, by trial and error, you can dial in the exact size.
    Tucson, AZ
    16x36 rectangular (19k) Pebble Tec play pool/spa, Pentair Intelliflo VS 011018, Super II 2hp (spa), Aqua Rite T-15 SWG, Pro Grid 60 DE, Hayward H400 & Heliocol Solar heating, A&A infloor system, fill water w/high CH and TA, 50 ppm borates,TF-100 test kit

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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Using change in FC level to measure pool size

    As others have said, you can get an idea of the pool size based on chemical additions. BUT, not just this single data point. For adding chlorine you have 2 independent variables: 1. pool volume and 2. bleach strength. Both would affect the FC ppm rise.

    In reality, there is no need to be exact on the pool volume.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
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  6. Back To Top    #6

    Re: Using change in FC level to measure pool size

    Great. Thanks everyone for the quick response.
    15K gal, IG, Pentair WhisperFlo, Cartridge Filter

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