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Thread: FAS-DPD Question

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    FAS-DPD Question

    I have been using the methods on this forum now for 3 yr and been getting great results. This year I have something new to me going on. When I try and measure the Chlorine I put the 10 ml of water then the scoop in. It turns a little pink in parts and when I swirl it goes completely clear. This is 20 min after adding 6 gal of bleach to a 30,000 gal pool so I would think it would have some amount of chlorine at this point. I thought the chem might be old so ordered replacement reagents and I'm getting the same results. The normal test in a taylor kit shows that there is Chlorine in the pool. I tried diluting the water till it read 2.5 on a taylor then tried the fas-dpd test on the diluted water and didn't get a good reading.

    CYA 45
    PH was way low took 7 boxes to raise up and now a touch high at close to 8. Water is looking good with only a slight green cast to it so was thinking that a day at shock level would finish the job.
    Vinal 30,000 gal
    Leslie's pool service test kit
    Sand filter
    2-skimmers

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    Richard320's Avatar
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    Re: FAS-DPD Question

    You've bleached out the FAS-DPD powder. Add another scoop.
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    Re: FAS-DPD Question

    That would make sense if the diluted sample would have read correctly but it didn't. It shouldn't bleach out with a standard test reading 2.5 should it?
    Vinal 30,000 gal
    Leslie's pool service test kit
    Sand filter
    2-skimmers

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    Re: FAS-DPD Question

    I can't follow the dilution thing but Richard is correct. If you put in the powder and it doesn't stay pink, you have not added enough powder. Put in another scoop and it should stay pink.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    JasonLion's Avatar
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    Re: FAS-DPD Question

    If you have an OTO chlorine test (drops turn the sample various shades of yellow which is compared to a color chart), test the water with that. If the OTO test shows zero chlorine then there really is zero chlorine. It is unusual, but the FAS-DPD test sometimes gives a false zero.
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    Re: FAS-DPD Question

    Jason,

    I think that's what OP has tried here....
    The normal test in a taylor kit shows that there is Chlorine in the pool.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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