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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. - Forum owner
    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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