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Thread: Bad dpd powder??

  1. Back To Top    #1

    Join Date
    Jul 2012
    Forest, VA

    Bad dpd powder??

    My pool has been burning through some chlorine the last two days and the deep end was a touch cloudy, so I did the OCLT test last night and lost 1-1.5 FC. So I figured I should start a SLAM. I tested this afternoon
    FC 3.5
    CC 0.5
    Cya 50
    Alk 110
    pH 7.5
    According to cya I needed to bring up to 20. So I added 2 jugs of 8.25% bleach. Waited 45 mins and retested. Halfway through the test (20 drops) the sample turned dark grey or black. I kept adding drops up to 40 and no change in color. It was bright magenta to start. Dpd powder is a few years old. Is my powder bad? Also tested cya after bleach and it said 40. Does the bleach affect the cya test? If not what can account for this? I need a solid cya number so I know what bleach to add. Please help and thanks for any replies.
    12,000 gal Octagon vinyl in-ground pool. Hayward S220 sand filter 3/4 hp pump, heat pump heater

  2. Back To Top    #2
    BoDarville's Avatar
    Join Date
    Jun 2012
    DFW, Texas

    Re: Bad dpd powder??

    Bleach will not affect the CYA test. The CYA test is one of the more subjective tests. Proper lighting is crucial when performing this test. Suggest referring to the Extended Test Kit Directions - see post # 8.

    If your DPD powder is a few years old, I would suggest replacing it with a fresh batch. In all the years I have performed this test, I have never had the sample turn grey / black.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

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