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Thread: Chlorine numbers are way off

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    Chlorine numbers are way off

    Here's the deal: Pool is clear, but for the last couple of weeks, chlorine numbers have been in the .5 - 1. range for FCL and .9 - 1.6 TCL. My CYA was at 30 so I added 6# to raise it to approx. 60PPM, it's at 38 today. Yesterday, I added 2.5 gals of 12.5% shock and 3# of powdered shock since the pool was cloudy and the numbers were so low. During the night the SWG worked for 8 hours (at 70% output) adding more chlorine to the pool. This morning the FCL was.06 and TCL was 1.2. What happened to my chlorine? I expected to be in the teens still. Pool pump runs 24/7 for a turnover of approx. 21k per 24 hours.

    Fiberglass 20k, SWG and sand filter.

    FCL 0.6
    TCL 1.2
    Ph 7.6
    TA 90
    CH 260
    CYA 38
    Salt 3.4k

    I'm stumped. I was told it's chlorine lock and advised to use 6# of an oxidizing shock to break this situation. Any suggestions?

    20k Leisure Pools 15' x 38' Moroccan fiberglass pool, plumbed with 2" lines all around, running a Pentair VS+SVRS pump and SD-70 sand filter, Compupool CPSC-36 SWG and a Watertech Blue Diamond robotic cleaner. Located in Central NJ.

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    Re: Chlorine numbers are way off

    You need to follow the Slam procees. See pool school for instructions.
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    Join Date
    Jun 2012
    Howell, NJ

    Re: Chlorine numbers are way off

    Chlorine lock doesn't exist. What does exist is organics (like algae) growing in your pool constantly eating your chlorine. What you need to do is order one of the recommended test kits (linked in my signature) and then SLAM the pool (also linked in my signature).
    7 year old ~13,500 gal 24' AGP with 1.5 hp Proline pump, 150 sqft Pleatco cartridge, filled with well water with pH of about 4.5.
    Wanda the Whale pool vacuum, home made heater, Taylor K-2006
    Cloudy Pool? 1) Order test kit. 2) Follow SLAM
    New to TFPC? Read Pool School a few times, then post questions. PoolMath will help with chemical additions.

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    In the Industry

    Donldson's Avatar
    Join Date
    Jun 2009
    NW Ohio

    Re: Chlorine numbers are way off

    Firstly, Chlorine Lock is the pool industry equivalent of Gremlins. When they tell you that they either don't have a clue or don't want to explain what is actually going on. I always assume the former.

    The numbers you posted are very suspect, I'm guessing pool store testing? First thing is that if you have added stabilizer, whether it shows up on the tests yet or not assume the CYA is in there, so treat your pool as if it the CYA is 60. We need to know what the active ingredient of the 3 pounds of powder "shock" you added was, do you still have the bags?

    Since your chlorine is hanging low there are organics, most likely the cloudiness is algae that is about to become a big problem. Do read about the SLAM process and make sure you have everything you need to do that. A traditional shock prescribed by the pool store will not be appropriate here, especially since they appear stumped and telling you it's chlorine lock.
    JD - 28' Round Above Ground Pool, 17,000 Gallons. Dual speed Jacuzzi pump with cartridge filter. Dual speed 1 HP pump, Hayward S210T sand filter
    Pool School - PoolMath - HIGHLY Recommended Test Kits

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