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Thread: Variable FC levels by different test kits, who to believe?

  1. Back To Top    #1
    ctakim's Avatar
    Join Date
    May 2012
    Phildelphia, PA

    Variable FC levels by different test kits, who to believe?

    Checked the pool chlorine 3 different ways today. By the TF-100 my readings were as follows:

    FC 4.5 (by FAS-DPD)
    CC 0.0
    pH 7.8
    TA 90
    CH 230
    CYA 35

    That all looks good but to make a comparison I also did the Basic OTO TC test using the Taylor K-1000 kit included with the TF-1000 and that gave me a reading of TC at 2.0??? Also checked an AquaChek strip and that gave me a reading of 5.0

    So how much chlorine do I have in the pool? 4.5 or 2.0? I presume the FAS-DPD is the gold standard but not sure why the OTO test was so poor? The strips might be better for a daily chorine check and reserve the FAS-DPD for once per week.
    Crackin' Toast, Grommit!
    29,000 gallon in ground, white plaster, with spillover Spa with 6 jets, 1 hp pump, Jandy DEV-60 DE Filter, Raypak 406a 400K Natural Gas Heater, Baracuda S3 Robotic, Jandy Aqualink RS4, TF-100 Test Kit
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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Variable FC levels by different test kits, who to believ

    I would trust the FAS-DPD above everything.
    The next strip you try might be completely different from the stories we have seen ... fine today, but might be wrong tomorrow.
    Not sure why the OTO appears to be off.
    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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  3. Back To Top    #3
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Variable FC levels by different test kits, who to believ

    OTO is never especially precise. OTO is perfect for determining if you have no chlorine, or some chlorine, or lots and lots of chlorine, but essentially useless for determining exactly how much chlorine you have.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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