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Thread: Precipitating Iron?

  1. Back To Top    #1

    Join Date
    Feb 2014
    Phoenix, AZ

    Precipitating Iron?

    Hi Gang,

    I've been trying to lower my TA and it seems like I am precipitating something out of the water. I think it might be Iron, but figured I would see if anyone here can support or destroy that theory :
    FC 8
    CC 0
    PH 8
    TA 190
    CH 525 ( Phoenix has crazy hard water ) - pebble tec finish on pool
    CYA 55**

    I've taken the PH down from 8 to 7 twice now with MA and that swing seems to precipitate out a fine red-brown powder. it's most pronounced at the lowest PH levels and as the PH creeps up, the precipitate rate slows down. I brush daily, so there has not been any staining, which I guess is thankful. The DE filter picks it up, and I've backwashed twice to get rid of it.

    The Phoenix Water test report shows
    Alkalinity 117 - 187 ppm
    Iron 0-7 ppb
    Sodium 73-194 ppm
    TDS 328-774 ppm
    Hardness 190-289 ppm

    I just did a 90% drain/refill with tap water to lower my CYA to that 55 level ( should have gone to 95% drain I guess ) so the water is almost all 'tap water'. I guess it could be some other thing, but I've had the chlorine drifting down from 20 to it's 8 level over the past week. I haven't detected CC in the past week, and did a .5 OCLT pass before letting the kids in the pool.

    I guess the easiest way to check if it's iron would be to use the strongest magnet I have to see how it reacts.

    So my question really is : is this normal / OK ?

    20k IG PebbleTec w/ STA-RITE PE5E-182L 1HP and Zodiac Polaris PB4 for Polaris 380 vacuum / Hayward ProGrid DE4820 Filter / TF-100 but I havent broken down and gotten a speed stir yet

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Precipitating Iron?

    It is worth trying the magnet, but I don't see how it could be iron. Iron might precipitate when the PH was suddenly increased, but lowering pH makes it more soluble. I suppose it could be some more complex reaction involving another chemical, but I can't think of one that would have that effect.
    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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