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Thread: Fas-DPD vs DPD

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    Join Date
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    Fas-DPD vs DPD

    I consistently get much higher readings with the fas-dpd method as compared to the dpd or strip methods. For example:
    fas-dpd dpd strip
    6.4 2-3 2-3
    5.6 2-3 2-3

    Is there a reason for this? Should I check my reagents?

    Mahalo
    10,500 gal; Hayward S244T sand filter GPM/FT 20; Intelliflo Vairiable Speed pump; 3/4 hp PAC FAB Challenger pump; IG; plaster ; CircuPool RJ60 SWG; Polaris 280 pool sweep

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    Mod Squad Bama Rambler's Avatar
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    Re: Fas-DPD vs DPD

    Trust the FAS!

    Color comparison is so subjective.
    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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    JasonLion's Avatar
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    Re: Fas-DPD vs DPD

    It is worth a double check to make sure you are doing the FAS-DPD chlorine test correctly. To get results by 0.2s and get the results you posted, you need to have been using a 25 ml sample and have added 28 to 31 drops to clear the pink. Is that what happened?

    For a residential pool there isn't any point in doing the test by 0.2s, you might as well do it so that each drop counts as 0.5. You will save reagent that way and get all the precision you really need.
    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

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    Re: Fas-DPD vs DPD

    I usually use 10 ml but was using the 25 ml to see if it might be more accurate. I've probably used the fas for over a year but whenever I do a comparison the dpd is always lower by what seems to me a substantial amount.
    10,500 gal; Hayward S244T sand filter GPM/FT 20; Intelliflo Vairiable Speed pump; 3/4 hp PAC FAB Challenger pump; IG; plaster ; CircuPool RJ60 SWG; Polaris 280 pool sweep

  5. Back To Top    #5

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    Re: Fas-DPD vs DPD

    I also can never get all the granules to dissolve, but I figured that they had you add more than probably needed
    10,500 gal; Hayward S244T sand filter GPM/FT 20; Intelliflo Vairiable Speed pump; 3/4 hp PAC FAB Challenger pump; IG; plaster ; CircuPool RJ60 SWG; Polaris 280 pool sweep

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    JasonLion's Avatar
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    Re: Fas-DPD vs DPD

    The powder shouldn't all dissolve. You always want to have extra powder. If you have too little powder there can be problems, but too much (within reason) is not a problem.
    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

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