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Thread: Quick test and FAS/DPD differ significantly

  1. Back To Top    #1

    Join Date
    Jun 2010
    Dripping Springs, TX

    Quick test and FAS/DPD differ significantly

    When I do a test with the color block apparatus, I am getting an FC reading of about 2.5.
    When I then do the FAS/DPD test from the TFT-100, I am getting an FC reading of 8.

    I believe the color block test more than I do the FAS/DPD right now, which is not the way it's supposed to work!

    I lost the small blue scoop used to put the powder in the test cylinder, so I have been estimating with a different small scoop.
    The amount of powder always struck me as pretty subjective anyway, but I'm wondering if this is where my problem is.
    When I put it in the cylinder to test FC, the water is a brighter shade of pink than I ever remember it. Is that a result of too much powder?

    I have had my kit for just over a year. Can the powder go bad?

    17K gallon IG freeform Pebble-Tec pool w/ raised spa/waterfall, Hayward 6020 DE filter, Tristar 1 HP circulation pump, Tristar 2.5 HP spa pump, Silencer 2hp blower, Aquarite SWG, Polaris 280 w/ booster pump, Hayward Universal H-Series 400K LPG heater, Ultrapure Ozonator 25, Aqualogic PS-8

  2. Back To Top    #2

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Quick test and FAS/DPD differ significantly

    Use the OTO test (color block/comparator) to test for the PRESENCE of chlorine but do not depend on it to test the amount accurately. Have faith in you FAS/DPD.

    The amount of powder used is not critical. You simply use enough that the solution turn pink/red.

    The brighter shade of pink would suggest a higher FC.

    If the DPD powder turns the solution pink, it is not "bad" and the test is valid.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  3. Back To Top    #3
    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    SouthWest Alabama

    Re: Quick test and FAS/DPD differ significantly

    I agree with Dave about trusting the FAS-DPD but to convince yourself, take a sample and dilute it with half chlorine free water and test it with both kits. See what you get that way.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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