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Thread: Second Chlorine Demand in two months?

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    Second Chlorine Demand in two months?

    I have had a pool for most of my adult life and have cared for it myself because I'm very picky about my water. I have a 32,000 gallon pool with a salt chlorinator.

    I returned from a 10 day vacation in June to a chlorine demand and decided it was easier to drain the pool then try to balance it. I have never had a chlorine demand in my life and wasn't exactly sure they existed (I do now).

    It seems like my pool is in another chlorine demand! Is this normal or am I missing something in the care of my pool? PH is 7.4, CYA is 50, but I'm using test strips since my son knocked over my regular test kit and stepped on it, so those are probably not accurate.

    I ran the filter for the last 24 hours after adding a huge amount of chlorine but even though my pool is now maintaining the chlorine level it is still cloudy? Any suggestions?

    I'm pretty much done with this pool this summer, fall can't come soon enough!!!

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    In the Industry
    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Second Chlorine Demand in two months?

    Welcome to the forum.

    What is your objective? You indicate you are done with the pool. Do you still want to get it clear or just close it?
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Mod Squad woodyp's Avatar
    Join Date
    Apr 2010
    East Texas

    Re: Second Chlorine Demand in two months?

    What is a "chlorine demand"? Is the pool green, algae growing, etc.? Has the pool been out of whack for 6 weeks or so? Welcome!
    16x32x52" Steel Cornelius Miramar AGP Vinyl liner 13,100 gal. Buried 2 ft.
    2 Speed Hayward Power-Flo Matrix 85 g.p.m. 22" 250lb. sand filter hard plumbed
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    Donldson's Avatar
    Join Date
    Jun 2009
    NW Ohio

    Re: Second Chlorine Demand in two months?

    What you are describing as "chlorine demand" sounds like what the industry calls "chlorine lock." If so there is some good news in that it really is a blanket term for a bunch of different problems, so if we can narrow down the specific problem we can help you fix it and prevent it from happening again. It doesn't really exist, if chlorine is disappearing then something in the water is causing that to happen. Algae, ammonia, bacteria, something.

    If you would like to fix it this season (not try, you absolutely can fix it if done right!) we would need a set of test results to see where you stand.

    We would also need to know what you used to get the results, how you typically chlorinate your pool, and what you use to shock it. If you use a powder to shock then we need to know the active ingredient in the powder. I know this is a lot of information but it is all necessary for us to make sure we steer you in the right direction.
    JD - 28' Round Above Ground Pool, 17,000 Gallons. Dual speed Jacuzzi pump with cartridge filter.
    Pool School - PoolMath - HIGHLY Recommended Test Kits

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    Re: Second Chlorine Demand in two months?

    Woke up this morning and the pool is beautiful again. I am curious what Is causing this as I would like to avoid it in the future. I used stabilizer and shock to get the chlorine back. (10 Bags!!!!) I will be getting a new test kit tommorow, I will post my readings then. Test strips have the FC at 3, PH at 7.4 and CyA at 50. These may be off as the color is hard to pinpoint exactly.

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    Join Date
    Jun 2012
    Louisville, KY

    Re: Second Chlorine Demand in two months?

    With one of the recommended test kits you will be able to really measure what's going on in your pool. When you dump shock product in it will knock what's growing in your water down, but not out. Hence it will just keep coming back which is likely what you're seeing.

    That's why we follow the SLAM process detailed in pool school if it's needed (and it sounds like you need it). That process of keeping and maintaining elevated free chlorine levels as long as it take to elminate organics in the water is what will fix any "chlorine demand" or "my pool won't hold chlorine" problem.

    In order to measure the FC levels required you need a test kit with a FAS-DPD chlorine test along with knowing your CYA. It's possible your CYA is much higher than you think meaning you are not maintaining a high enough FC level to sanitize the pool and keep algae at bay.

    Regarding the test strips - they are about worthless for any kind accurate of testing. You need a good test kit to take control of your pool.
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

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    techguy's Avatar
    Join Date
    Jul 2010
    Antelope, CA

    Re: Second Chlorine Demand in two months?


    What is the product in the 10 bags of shock? I am going to guess your CYA is going to increase unless your shock is a CalHypo based product, then your CH has changed.

    Understanding the relationship between CYA and chlorine is critical to the BBB process.
    -- Guy --
    10K gallons in 21' Round 52 inch wall Aqualeader AG, Hayward Power Flow LX 1.5 HP pump motor, Hayward Perflex EC50AC DE filter w/Cellulose, Wide mouth skimmer, 2013 new Diver Dan (craigslist) to replace the faded old Hayward AquaBug. TF-100

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