Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 6 of 6

Thread: DPD Powder

  1. Back To Top    #1

    DPD Powder

    When I got my first TF-100 test kit last year the powder was a light gray. I always keep my kit stored inside but even so, I'm in FL and humidity is high. I also have a few packets of silica gel I keep in my test kit thinking it should help with humidity.

    When I broke out the kit after the winter I noticed the powder had darkened, but I assumed it was still good. It seemed to be working fine and I never had a reading of more than .5 CCs. But last week (my bad) I let the FC drop to 2 and I got a touch of algae. Still, my CCs tested <1. I brushed and shocked the pool and the FC held overnight on the first night. Since then I have been waiting for the chlorine to drop back to maintenance level before turning the SWG back on. No one has been swimming because we're both sick so it has taken a while.

    Anyway, today I broke out the new powder I just received and was surprised to see it is a white color. When I tested I had a reading of 1 CC, so I suspect the old powder I was using was not giving me a good reading of CCs.

    When the powder turns dark does that mean it is bad?
    What is the shelf life of the powder supposed to be?
    Sue

    18' round Sharkline Matrix AGP / 8600 Gal. / sand filter / Aqua Trol SWG
    Pool owner since 2001. Thanks to TFP for helping me convert off Baquacil after six years!

  2. Back To Top    #2
    SeanB's Avatar
    Join Date
    Mar 2007
    Location
    Missouri City (suburb of Houston, TX)
    Posts
    2,622
    Normally it turns from light grey to a purplish color, but that does not change the effectiveness. If it's been kept indoors and closed it should last for a couple of year, maybe more. I've not heard anyone mention theirs turning white though.

    If you can post up your full set of numbers, we might be able to get a better idea of what's going on.
    TFP Founder

    My Pool: 13K gal IG gunite with 7' spa, Pentair Cartridge Filter, Intellichlor IC40 SWG, Polaris 280 Cleaner, TF-100 Test Kit w/ salt test.

  3. Back To Top    #3
    The powder that was white was a brand new jar.

    My numbers:
    FC 3.5
    CC 1
    pH 7.2
    TA 100
    CYA 55 (added one cup on Monday after testing... trying to get to 60)
    SWG was turned back on after testing today.
    Sue

    18' round Sharkline Matrix AGP / 8600 Gal. / sand filter / Aqua Trol SWG
    Pool owner since 2001. Thanks to TFP for helping me convert off Baquacil after six years!

  4. Back To Top    #4

    In the Industry
    duraleigh's Avatar
    Join Date
    Apr 2007
    Location
    Sebring, Florida
    Posts
    28,395
    Sue, I think you were originally talking about the difference in your test results (.5cc vs. 1.0cc).

    That's one drop difference and it's my experience that's about as close as you can get it. The test will vary that much from day to day. I have used some dark powder that's over four years old and the results have always been valid. It doesn't take long for it to turn light grey and then that dark purplish grey but it still seems to work.

    Taylor says replace it every year and I can't say not to. My experience tells me you can go longer than that, however.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  5. Back To Top    #5
    okie dokie. When I saw that the new powder was white it just kind of made me wonder.
    Sue

    18' round Sharkline Matrix AGP / 8600 Gal. / sand filter / Aqua Trol SWG
    Pool owner since 2001. Thanks to TFP for helping me convert off Baquacil after six years!

  6. Back To Top    #6
    Guest
    The powder reacts with moisture and atmospheric oxygen and darkens in a very similar way that an open bottle of permanent haircolor turns dark once it has been opened. (Not surprising since DPD is one of the dye bases used in some haircolors). It does lose a bit of 'potency' as it darkens (oxidizes, actually) but as long as you are getting a good pink color when you add it to your sample of pool water it will work fine in much the same way that an opened bottle of hair color will still color the hair properly even though it has darkened in the bottle. Some of the active ingredients has oxidized but there is still a lot of unoxidized material present.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •