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Thread: Getting inconsistent fas/dpd results.

  1. Back To Top    #1

    Join Date
    Jul 2013
    Winchester, KY

    Getting inconsistent fas/dpd results.

    I'm still getting the hang of doing the test with the tf test kit. I've learned how to get consistent drop sizes with the reagent. And I use enough dpd powder. And I use 5 drops of r0003 to test for CC. But here's the situation I'm having now.

    Tested the water this morning and got FC - 3.5. CC - 1. TC - 4.5

    Tested two more times immediately after the first test and both times got, FC - 4.5. CC - 0. TC - 4.5.

    It has been like this since I started testing this year. What am I doing wrong? Is it possible the the r0003 is remaining in the graduated cylinder from the first test and causing me to effectively test for the TC in subsequent tests?

    I also just got a speed stir so I don't imagine that I'm swirling the test wrong since it's done automatically now.

    Thanks for any input you all have!!
    26,660 gallon, in ground pool vinyl pool. Hayward S-200 Series Sand filter. Flow Rate 44GPM

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Getting inconsistent fas/dpd results.

    There are two things I can think of that could cause that. The first is taking too long when doing the test. CC can "leak" into the FC portion of the test if you take too long. However you would need to be going rather slowly for that to happen. Second, are you sure the sample is turning completely clear? Towards the end of the FC portion of the test the sample can be a very pale pink that doesn't show up well. If you miss that pale pink and continue on to the CC portion of the test, some of the FC reading will be read as CC.
    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

  3. Back To Top    #3
    bridgman's Avatar
    Join Date
    Mar 2014
    Bowmanville, ON Canada

    Re: Getting inconsistent fas/dpd results.

    If you're not rinsing the cylinder out thoroughly with tap water *after* the test and rinsing with a bit of sampled pool water at the start of the next test give that a try.
    Cedar hot tub, 680 US gallons - Snorkel wood-burning heater, canoe paddle, "offline" Intex 1000 GPH pump/filter with skimmer

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