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Thread: Mixed chlorine results between quick test and "drop"

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    bdenehy's Avatar
    Join Date
    Mar 2008
    Putnam Co., NY

    Mixed chlorine results between quick test and "drop"

    I'm new to testing my own water and am using the TF-100. It's all straightforward but I'm getting mixed chlorine results. The daily "yellow tests" gives me a TC of around 3 and the R-870 shows a pretty consistent 4.5 to 5.0 FC and 0 to 0.5 CC. I took my last test to the pool store to verify and they show 3.6 for FC and TC. All my other results were pretty close to theirs. Any tips on closing the gap/getting closer results? I have a SWG so I'm not sure if the difference is a big deal but don't want the chlorine too high (I've got little kiddies that can't wait to get in the pool).

    Thanks for any help. This site is Great!!!

    My Test
    FC 5.0
    TC 5.0
    PH 7.2-7.5
    TA 90
    CH 110
    CYA 45

    Pool Store
    FC 3.6
    TC 3.6
    PH 7.2
    TA 84
    adj TA 69 (any idea what the diff is?)
    Tot. Hardness 79
    CYA 50
    35,000 gal vinyl, Hayward DE Filter, Hayward 400k BTU heater, SWG, Polaris 380 w/booster pump, plenty of dog hair in the skimmers.

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD
    I would believe the FAS-DPD test, it is more precise and more difficult to do wrong. I find the OTO chlorine test (shades of yellow) to be difficult to read between 3 and 5, anything in there looks like three to me. Also, it is not uncommon for some of the chlorine to "vanish" on the way to the pools store, which could account for their result.

    You don't need to worry about adjusted TA. We don't normally use that around here. It is only important if you are trying to calculate LSI, which you have no reason to do.
    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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