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Thread: Question about FAS-DPD testing

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    Question about FAS-DPD testing

    I've been using the FAS-DPD test kit daily for a couple of weeks now and the results I've been getting are very consistent so I've gotten a little lazy and I'm wondering if that's bad.

    Every evening, I test my chlorine and it's somewhere between 5 and 7 and I add enough to raise it to 8. Given that I'm always between 5 and 7, I've gotten in the habit of immediately adding 8 drops all at once (to get me up to 4), swishing it around real good and then starting to count 1 drop at a time. Is there any reason that's not a good idea (other than if it happens to go clear after 8 drops, I have to throw everything out and start all over)?
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    20,500 gal gunite pool w/ PebbleTec and infloor cleaning system.
    Sta-Rite System 3 cartridge filter.
    Houston, TX

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    reebok's Avatar
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    Re: Question about FAS-DPD testing

    waterbear has said on multiple occasions that you shouldn't do it that way. I used to do it that way and then I stopped. if you're consistent in your losses, and you aren't afraid of testing less often, you can just add about 2ppm each evening and test every other day or whatever you decide on.
    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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    Re: Question about FAS-DPD testing

    Thanks.. I figured the question had been asked before, but couldn't come up with search terms that would locate it!
    ----------------------
    20,500 gal gunite pool w/ PebbleTec and infloor cleaning system.
    Sta-Rite System 3 cartridge filter.
    Houston, TX

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    37,887

    Re: Question about FAS-DPD testing

    It is very important on the CH test to not add more than one drop at a time. But on the FAS-DPD test, it doesn't really matter (unless it turns clear and you don't know which drop that would have happened on).

    Many people just use the simpler OTO chlorine test for daily checks. If it is about the right shade of yellow, assume everything is good. Any major problems will be apparent, though small errors could be missed. As long as you do the FAS-DPD test at least once a week that is generally good enough.
    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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