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Thread: Question about FAS-DPD test for CC

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    Question Question about FAS-DPD test for CC

    I have a question about the FAS-DPD combined chlorine (CC) test, in the Taylor kit. I'm using the sample size where each drop represents 0.2 ppm of chlorine. I did the FC test first, and the pink color completely disappeared after 18 drops, indicating the FC is 3.6 ppm.


    Then I added 5 drops of reagent R-0003, to test for CC. The sample just barely turned pink. Viewing it from the side it appeared clear, but when I looked straight down into the tube it was just barely detectable pink. The instructions do not tell you to look straight down into the tube when doing the CC test, but that's the only way I could detect the very faint pink tinge.


    When I added 1 drop of R-0871 and swirled, the pink completely disappeared. So I figured that means I have some CC but no more than 0.2 ppm. However after several minutes, I noticed the very faint pink color had returned. So I added one more drop of R-0871 and the pink completely disappeared again. So I figured that maybe I have 0.4 ppm of CC. But after several more minutes, the faint pink color returned, and if I waited even longer it got more noticeable.


    So I can't tell how much CC I really have. The test kit instructions do not say anything about waiting any period of time when doing the CC test. Should I just count the number of drops needed to initially get rid of the pink and ignore the fact that it returns after several minutes? As I said, after I add the 5 drops of R-0003, and swirl, the pink color is so faint it is only visible when looking straight down the tube.


    As background, my CYA is about 45, pH=7.6, TA=100. The pool was refilled a couple months ago and everything else is in a good range. I'm only using bleach and I've been consuming about 3 ppm of FC daily, mainly due to sunlight (no swimmers for the last few days). I add enough to get FC up to about 6 to 7, and then it's down to 3 to 4 by evening. So I think I'm maintaining FC correctly, but it's the CC test that puzzles me. We did have a lot of swimmers 5 days ago so I figured i might have some CC from that, but I can't tell how much.
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit

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    pabeader's Avatar
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    Re: Question about FAS-DPD test for CC

    It is normal for the color to change back to pink after testing. That's why we recommend that the tests be done one after the other. Once you have your result, you can dispose of the sample.
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: Question about FAS-DPD test for CC

    Quote Originally Posted by RGS View Post


    Then I added 5 drops of reagent R-0003, to test for CC. The sample just barely turned pink. Viewing it from the side it appeared clear, but when I looked straight down into the tube it was just barely detectable pink. The instructions do not tell you to look straight down into the tube when doing the CC test, but that's the only way I could detect the very faint pink tinge.


    When I added 1 drop of R-0871 and swirled, the pink completely disappeared. So I figured that means I have some CC but no more than 0.2 ppm. However after several minutes, I noticed the very faint pink color had returned. So I added one more drop of R-0871 and the pink completely disappeared again. So I figured that maybe I have 0.4 ppm of CC. But after several more minutes, the faint pink color returned, and if I waited even longer it got more noticeable.

    CCs are minimal... good thing...

    I had the same issue with my taylor until I realized the bottom of the tube is white...creating a great contrast for any pink tinge.. would be nice to have that somewhere on the box.. Hopefully Taylor is listening...
    Inherited 24' Muskin Above ground
    13500 gal
    Hayward S180T92S Sand filter
    Taylor K-2006C Speedstir
    TFPC for Beginners | Pool Math | Pool School | CYA Chart | SLAM | Test Kits | ABC's

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    Re: Question about FAS-DPD test for CC

    Quote Originally Posted by pabeader View Post
    It is normal for the color to change back to pink after testing. That's why we recommend that the tests be done one after the other. Once you have your result, you can dispose of the sample.
    Thanks. I did do the CC test immediately after the FC test, so the clear water from the FC test had not changed back to pink yet. It was a few minutes after the CC test that I noticed it had gone back to a slight pink. I know now that i can disregard that. My CC does seem to be no greater than 0.2, so I'm happy.
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit

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