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Thread: Suddenly low chlorine usage...good, but why?

  1. Back To Top    #1

    Join Date
    May 2013
    Rockwood, Michigan

    Suddenly low chlorine usage...good, but why?

    I changed over to pool school methods at start of year and am having my first perfect pool season in years! got cold in Michigan 3rd week of July so I started using new solar cover for 1st time in a couple seasons.
    Following recommendations, I target FC=6 for CYA=55. CC all season has been 0.25 since first passing overnight test.
    That has all meant pouring in about 75 ounces of 12% bleach daily...such that it became habitual.
    When I put solar cover on, I kept up that routine for the course of a few days.
    Then I checked chemicals and my chlorine had spiked high!
    I didn't put chlorine in for few days until it got back down, then I did full check.
    CYA=50 FC=4.5 and CC=O.0
    First time all season CC=0!
    Then daily checks, solar cover on every night and probably stays on 3 days per week.
    In the last 10 days, I have used only 1.5 gallons of 12% bleach to maintain proper FC level in pool.
    All other checks are perfect. Pool water is perfect. It all seems too good to be true.
    I certainly don't want to jinx it, but is there a logical explanation for my extremely low chlorine usage?
    Pool: 24,000 gallons, IG, Plaster, Sand Filter, 3/4 HP Pump, Year 2000 Install, Polaris auto vacuum, Lochinvar Heater

  2. Back To Top    #2
    pwrstrk's Avatar
    Join Date
    Aug 2012
    Elverson Pa.

    Re: Suddenly low chlorine usage...good, but why?

    The solar cover will help some with FC loss from the sun and also not swimming as much will consume less FC

    Less FC loss is a good thing. Sometimes with my cover on I only lose 1-1.5 ppm a day. My cover is clear also.

    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

  3. Back To Top    #3
    BoDarville's Avatar
    Join Date
    Jun 2012
    DFW, Texas

    Re: Suddenly low chlorine usage...good, but why?

    The cooler weather (and cooler water temps) also tend to help lower FC loss. I have noticed this over the past couple of days here due to the cooler weather and water temps compared to last week when air temps were in the 100's. In my case, this is the only variable that has changed.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
    A good test kit is an investment, not an expense.

  4. Back To Top    #4

    Join Date
    May 2013
    Bay City, Michigan

    Re: Suddenly low chlorine usage...good, but why?

    exactly what was said above, the solar cover during the day lowers FC loss, the colder water lowers FC loss also. Haven't been in our pool here in Michigan since the heat wave many weeks ago. (no heater) Our pool is 12500 gallons (half the size of yours) and only use 16 oz a day (covered and unused) and still ended up getting higher than I was targeting.

    Now during the MI heat wave, our water was too warm and was leaving the cover off all day/night and because of the warmer water and no cover, had to use 64 oz to 80 oz a day. (16oz = 1ppm for me)
    12500 gallons, 24 foot round above ground
    Hayward Sand filter, Pentair OptiFlo 1HP 2-Speed pump

  5. Back To Top    #5

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Suddenly low chlorine usage...good, but why?

    Overall chlorine reaction rates double every roughly 12F temperature rise. So conversely, they slow down significantly as the water temperature drops. Because I have a mostly opaque solar cover, I can see the chlorine loss rate drop from 0.7 ppm FC per day at 88F (when the pool is not used) down to 0.071 ppm FC per day (1 ppm FC every 2 weeks) at 50F over the winter.
    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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