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Thread: Chlorine demand

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    ivyleager's Avatar
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    Sep 2007
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    Raleigh-Durham,NC
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    Chlorine demand

    Is there a general time frame when water holds chlorine after ascorbic acid treatment? Also, my pH is continually rising. (assuming d/t all the bleach I'm adding).

    I'm going on 3 weeks post treatment and I STILL have bleach being consumed very quickly in my pool. I generally add bleach every other day. Today I added in the morning and evening.

    This mornings numbers at 8:30am: (I added 1.5 lg jugs of bleach around noon day before- raised 5-6 ppm).
    Water is crystal clear.
    FC 0
    CC 0
    TC 0
    CYA 50
    TA 80
    pH 7.6 (hardly moved after adding 4 c. muriatic acid - Home Depot brand, not very concentrated I think).
    CH 130

    To prevent algae, I'm running pump/filter 24/7 and used whole bottle of polyquat before AA tx, and am adding about 10 cc a week now. So far, so good.

    Just suprised that chlorine isn't holding.
    CaryB
    36 x 18 IG vinyl, 25K, 1 HP pump, sand filter
    1 skimmer, 2 returns, no main drain
    Old school: PoolSolutions test kit

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    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
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    Re: Chlorine demand

    It's not a timeframe, but rather an amount of added chlorine. One pound of ascorbic acid is equivalent to 100 fluid ounces of 6% bleach or 4.8 ppm FC in 10,000 gallons. If the ascorbic acid didn't get used up very much reducing metal stains (and it usually won't), then the rest will use up chlorine. Some of that chlorine is what you started out with when adding the ascorbic acid and much of the excess will consume chlorine that gets subsequently added. So if you know how much ascorbic acid you added and know the FC level when you started, you can calculate the worst-case amount of FC you'll need to add to have it start to register again. That assumes that algae growth hasn't started.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    ivyleager's Avatar
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    Sep 2007
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    Re: Chlorine demand

    No algae growth at all. I'm running filter 24/7, using Aquabot 5 hr/day to keep things clean, and making sure to add polyquat weekly. I'm making sure I have 4ppm chlorine in water as much as possible, testing 2x/day. Don't want to end up needing to superchlorinate yet, per mbars guidelines.

    I used 2# of AA for my 23K pool. Chlorine was zero when dumped it in. I've used 5# of Cal-hypo and 12 lg. jugs of bleach so far. So based on your calcs above, I should be more than done. Here's hoping!
    CaryB
    36 x 18 IG vinyl, 25K, 1 HP pump, sand filter
    1 skimmer, 2 returns, no main drain
    Old school: PoolSolutions test kit

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    37,879

    Re: Chlorine demand

    You always need more than the calculated amount due to additional chlorine getting used up breaking down organics and lost to sunlight.
    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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