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Thread: FAS/DPD Test

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    DonW's Avatar
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    Jun 2008
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    FAS/DPD Test

    I have a question about the FAS/DPD test. My test kit arrived in the mail today and was anxious to use it for the first time because I suspect an algae bloom in progress. I have had stains on the floor that resemble bird droppings, yellow/brownish/greenish in color and greenish staining happening along a small portion of the cove in places. My skimmer sock has a vibrant green color to it and washes out o.k., but my thermometer string has turned green. To be honest I've been shocking the pool with triichlor shock and have been using the pucks. My CYA has shot way up and now I am on the precipice of being a full-blown BBB convert. I have bought 16 gallons of bleach and am going to shock tonight with that. It appears from the calculator I'm going to need about 6-7 gallons to begin. I'm even leaning towards a partial drain-down after this so I don't have to use so much bleach in the future.
    My question: When testing for CC's and you are adding R-0871, will the sample remain clear, or after awhile, say 20-30 seconds, return to pink? I have been adding the R-0871 and counting. I go to mark my results down and when I look up the sample has turned pink again!
    I have been running the pump 24/7 since I've suspected the algae, and the water is clear with minimal staining. I've been waiting for the FAS/DPD test kit to arrive before I started to shock with bleach. My numbers are:
    FC: 7
    TC: > 4
    PH: 7.5
    ALK: 250
    CYA: 75-80

    Any other data to provide I do not know or cannot test for. Sorry this has been long-winded but I wanted clarification on the drop test. This has been a great site and I've learned so much from it. It's taken awhile, but the conversion from trichlor to BBB will happen tonight. My apologies to all for being resistant, but there has been an awakening!
    18' x 33' AGP
    16,715 gal.
    200 lb. Sand Filter w/Hayward PowerFlo MATRIX 1.5 H.P. 2 Spd. pump
    Stenner Injection Pump System

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    JasonLion's Avatar
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    Re: FAS/DPD Test

    If you are going to lower CYA, it is much better to do that first and then shock.

    When doing the FAS-DPD chlorine test, if you leave the sample sitting after you are done it will turn pink again. Normally this takes more than a minute after you are done, but if the test takes a while to perform it can happen sooner.
    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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    reebok's Avatar
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    Re: FAS/DPD Test

    it will turn back pink. do your tests as instructed on the form. when it's clear, you're done, just pour it out at that point if it will be less confusing.
    if you're going to drain, do it now rather than later. you'll save money right away by using less bleach.
    so what is your CC number? btw, TC=FC+CC
    16x32 21,000 gallon in-ground exposed aggregate, 1.5hp pump, 120 sqft catridge filter, birdcage, solar panels, aquavac tigershark qc robot.

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    DonW's Avatar
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    Re: FAS/DPD Test

    Thank you to both for the quick reply, clarification and tip. I did make one mistake in that for TC should have been CC. I'll do the test one more time for practice/assurance as the need to shock is evident.
    18' x 33' AGP
    16,715 gal.
    200 lb. Sand Filter w/Hayward PowerFlo MATRIX 1.5 H.P. 2 Spd. pump
    Stenner Injection Pump System

  5. Back To Top    #5

    In the Industry

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    Re: FAS/DPD Test

    Sorry the need to re-read Jason's post is more evident.
    Partial drain down to lower CYA then shock.

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