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Thread: FC Test with less chemicals

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    FC Test with less chemicals

    Is it accurate to do an FC test using 1 scoop and 5ML water sample and counting each drop of R087 as 1 ppm FC? My FC is at about 13 and it seemed to work well. Thoughts?
    21,500 Gallon Vinyl liner pool Eastern Pennsylvania
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    Mod Squad kimkats's Avatar
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    Re: FC Test with less chemicals

    I use one rounded scoop of powder but have never tried the 5 ml of water. Have you done a back to back test with the 10ml of water and 5 ml to see if they "match"? I think the 10ml uses little enough regents I do not worry about it.

    Kim
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    Mod Squad JVTrain's Avatar
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    Re: FC Test with less chemicals

    Keep in mind, any time you use less volume, the precision of the test is decreased.

    From Pool School - FAS-DPD Chlorine Test
    The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.
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    Re: FC Test with less chemicals

    Quote Originally Posted by JVTrain View Post
    Keep in mind, any time you use less volume, the precision of the test is decreased.

    From Pool School - FAS-DPD Chlorine Test
    The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.
    Right, so to illustrate, if you are using the 10 ml sample your error rate will be +/- 0.5 ppm up to 5 FC, 1 ppm at 10 FC, and 2 ppm at 20 FC. If you are using the 5 ml sample then your margin of error is double that. So a reading of 13 means your FC is between 10.5 and 15.5 (rounded).
    JD - 28' Round Above Ground Pool, 17,000 Gallons. Dual speed Jacuzzi pump with cartridge filter. Dual speed 1 HP pump, Hayward S210T sand filter
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    Re: FC Test with less chemicals

    Quote Originally Posted by Donldson View Post
    Right, so to illustrate, if you are using the 10 ml sample your error rate will be +/- 0.5 ppm up to 5 FC, 1 ppm at 10 FC, and 2 ppm at 20 FC. If you are using the 5 ml sample then your margin of error is double that. So a reading of 13 means your FC is between 10.5 and 15.5 (rounded).
    Maybe I am getting huge errors and that is my issue... doesn't seem to accurate at that rate... hmmm.
    IG, 25k gallons, 20x40 ft, Plaster, Pentair sand filter, variable speed pump, have a well, TF-100 test kit, Speed Stir

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    Re: FC Test with less chemicals

    Okay thanks for the input. I have been using 1 round scoop of powder and 10ML water sample, but I tried it with 5Ml and got the same results, so that is why I posted the question. Seeing that the margin of error increases I will stick with the 10ML water sample. Thank you for all the responses.
    21,500 Gallon Vinyl liner pool Eastern Pennsylvania
    Hayward 2 HP pump 2" Pvc pipes Full Sun Pool
    Hayward sand filter, Compupool CPSC 48 SWG
    12mil solar cover and reel

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