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Thread: DPD Chlorine test strange

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    DPD Chlorine test strange

    I was going to leave the pool circulating this winter and unforseen reasons have me scrambling to winterize it instead. The wife brought the chlorine level up to shock she thought but when she tested the water the test vile turned light pink and then immediately went clear before adding any chemical at all. Never saw this before. We know there is enough chlorine to get it up to a 24 reading but this is what we are seeing. The water is quite cold. Does this have anything to do with it? Call me stumped!
    27 foot round above ground

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    JasonLion's Avatar
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    Re: DPD Chlorine test strange

    If you are using the regular DPD chlorine test, drops added to the sample turn it various shades of red/pink, which are then compared to a color chart: the test is prove to bleaching out at high FC levels, so clear can indicate that the FC level is quite high, which fits with your description. You can avoid this problem by mixing equal parts of pool water and chlorine free water (for example distilled water), testing that, and multiplying the results by two.
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    UnderWaterVanya's Avatar
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    Re: DPD Chlorine test strange

    What test kit? If you are using the regular DPD test not the FAS-DPD, that's normal. The DPD test is a color shade matching test with pink colors. The FAS-DPD test is a color change test that has a powder you add then drops you count.

    The simple DPD test can go colorless at high FC levels. You can verify this if you have distilled water. Dilute the sample with equal parts pool water and distilled water. If still clear try two parts distilled water to 1 part pool water and if that is still clear you can try 3 parts distilled water to 1 part pool water. The numbers you see on your test get multiplied by the total number of parts. (1 part of each is two total parts thus 2x what the kit reads).



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    UnderWaterVanya's Avatar
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    Re: DPD Chlorine test strange

    Jason beat me with his typing.


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    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

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    Re: DPD Chlorine test strange

    It is the FAS-DPD test I think using the DPD 0870 powder.
    27 foot round above ground

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    Mod Squad Bama Rambler's Avatar
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    Re: DPD Chlorine test strange

    If you have an OTO chlorine test use it see what color it turns.

    On your FAS-DPD test try adding 2 scoops of the R-0870 powder and see if it stays pink.
    Dave J. TFP Moderator
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    Re: DPD Chlorine test strange

    Will do on the FAS-DPD test. Thanks for the tip. Do I just proceed with the test then as normal?
    27 foot round above ground

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    Mod Squad Bama Rambler's Avatar
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    Re: DPD Chlorine test strange

    Yes, if it stays pink just run the test normally.
    Dave J. TFP Moderator
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    Re: DPD Chlorine test strange

    It is staying pink. Is this due to water temperature?
    27 foot round above ground

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    Re: DPD Chlorine test strange

    My FC is almost twice what the pool calculator said it would be from the amount of chlorine it said to add. Wonder why? Do I half that due to adding two scoops?
    27 foot round above ground

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    Mod Squad Bama Rambler's Avatar
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    Re: DPD Chlorine test strange

    A couple of things come to mind. 1) She added more than the PC said to. 2) The chlorine was stronger than it should have been. 3) You had either the gallons or the starting FC wrong in the PC.

    Adding two scoops doesn't affect the accuracy of the test. The test is accurate so long as you add enough powder to bind all the chlorine. Adding too much doesn't matter. With such high chlorine you weren't adding enough to bind it with just one scoop.
    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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    Re: DPD Chlorine test strange

    Thanks for the info.
    27 foot round above ground

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