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Thread: Chlorine test method accuracy

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    Chlorine test method accuracy

    Testing for chlorine with the FAS/DPD test gives me results 2.5 times higher than the pool store, test strips, or color comparison liquid (OTO) tests. Bioguard analysis said 1.6% total chlorine, but the FAS/DPD showed 4.0%. Any help would be appreciated. Thanks
    27000 gal, sand filter, IG, 1988

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    Mod Squad JohnT's Avatar
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    Re: Chlorine test method accuracy

    You are filling to the 10ml line, adding a scoop of powder, counting the drops and swirling between additions, then doubling the number of drops for your reading?
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
    Hayward S244T Sand Filter with 1HP Whisperflo Pump. Liquidator C-201 and Solar Heat

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    Mod Squad Bama Rambler's Avatar
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    Re: Chlorine test method accuracy

    Welcome to TFP.

    Are you using the 25 ml sample or the 10 ml sample?
    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: Chlorine test method accuracy

    You can safely toss out the results from the pool store and the test strips.....they are worthless.

    The OTO test is never terribly accurate but it is always dependable.

    If you performed the test properly, the FAS/DPD result can be taken to the bank

    (It's ppm (parts per million), not percent)
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Chlorine test method accuracy

    Yes, 10 ml plus scoop of DPD, dropwise addition of FAS, multiply X 0.5. Having a chemistry education and career, I'm understandably curious about accuracy of test methods. So the statements of "worthless" or "take it to the bank" aren't as quantitative as I'd like. Nevertheless, I'll go with the FAS/DPD as the gold standard. thanks for the feedback. (Yeah, I know it's ppm not %)
    27000 gal, sand filter, IG, 1988

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    Re: Chlorine test method accuracy

    I was just like you when I started and finally gave up (trying to compare all the different test results) and committed to only using the FAS/DPD test and my pool has been perfect for 3 years
    35K IG Vinyl 20 x 40 self built pool, Hayward Pro Series High-Rate Sand Filter 31" 98gal/min, Hayward TriStar 1.85hp, Hayward 400btu heater, BBB method w/Hypo, Jazz light w/matching fiber optic rope lighting around coping w/syncronized color wheels. Concrete Paver deck.

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