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Thread: Need Help - Chlorine Not Holding

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    Need Help - Chlorine Not Holding

    Hi Everyone

    I'm a newby to the website, but heard this is the place to go if you have a problem. We have a 29,400 gallon inground vinyl pool with automatic cover and automatic chlorinator. We opened the pool two weeks ago and the water looks great, but we can't get a chlorine reading. We have shocked the water about four different times but still not getting a reading. This happened to us last year too, and after many many hundreds in chemicals we ended up draining the pool completely. (Last year there was a high CYA near 100), but we also had a chlorine demand issue. Here are our numbers from the pool store: Tot. Chlorine: 0.3, Free Chlorine: 0, PH: 7.1 - added 20 lbs of balance pak 100 per store to raise, Alkalinity: 61, Hardness 288, CYA: 0, TDS: 500. (P.S. I can't believe the CYA is zero because we use the Chlorine Pucks and I was told the CYA stays in the water, so we should still have it from last year). Any Advice would greatly be appreciated. Thanks Everyone

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    svenpup's Avatar
    Join Date
    Nov 2009
    Sacramento, CA

    Re: Need Help - Chlorine Not Holding

    Welcome to TFP!

    There is a documented phenomenon where CYA is converted to ammonia by bacteria. Read here for an example.

    Your chlorine demand is high because you need to oxidize ammonia as well as the other organics that have been allowed to build up because of the lack of FC.

    Your need to keep shocking. Remember, shock is a process, not a product. You should add chlorine as often as practical (as frequently as once per hour) to maintain shock levels.

    Read the shocking instructions in pool school.
    TFP Method Advanced Intermediate
    • 17,500 gallons - In Ground - Plaster - Hayward Swimclear 3020 Cartridge Filter - Sta-Rite Max-E-Glas Main Pump upgraded with A.O. Smith B2980 E-Plus New Centurion Two-Speed Motor - Polaris 280 Cleaner with Polaris PB4-60 Booster Pump - TightWatt2 Timer - Taylor K-2006 Test Kit - Pool Pilot Digital Nano SWCG

    Helpful Links: Pool School, BBB for Beginners, How to Shock ('s a process not a product), Chlorine/CYA Chart, Jason's Pool Calculator

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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Need Help - Chlorine Not Holding

    The ammonia issue svenpup refers to may not exist in your pool since your pool is indoors. That said, the lack of a CYA reading would lend credence to the ammonia forming.

    However, for simplicities sake, you need to add a lot more chlorine to your pool regardless. perhaps a LOT more chlorine.

    It would be a good idea to do your own testing or, at the very least, confirm the test results from a different pool store......don't be surprised if they vary a lot.

    One you post back confirmed results (I'm skeptical of that CYA test, like you) then we'll know a good path to proceed but it's going to involve a lot of Clorox in any case.....more than you realize. It'll probably also involve adding about 20ppm CYA if you are in fact at zero......just don't put any in until that's confirmed
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Need Help - Chlorine Not Holding

    I am not sure where we see it's an indoor pool...

    You should stay away from the pool store for advice. From what I've seen so far it's bad.

    Balance Pack 100 is baking soda, and is used to increase your TA, which at 61 was pretty good for a SWG. If they wanted to raise your pH, they should have given you Blance Pack 200 (soda ash). Borax would have probably been better... And this may not even be the right problem to be focusing on right now.

    Regardless, ammonia from CYA conversion certainly seems like a likely culprit, but you will need some good test results to proceed. While you are at it, you can stop at a pet store to get an ammonia test to take some of the guess work out of it.

    Also, let us know what chemicals you have on hand. Although it would be generally recomended to stay away from stabalized cholrine sources, like dichlor and trichlor, if your CYA is truely zero, now might be a good time to use it up if you have it. (We just have to be careful to keep track of everything, and test to make sure we don't over shoot CYA values).

  5. Back To Top    #5

    Re: Need Help - Chlorine Not Holding

    Thanks for all the Quick Responses

    Sounds like I just need to be patient and keep added chlorine/shock. I also appreciated the advice about reading the section on shocking my pool, it was very informative. I am going to head out and get a test for the Amonia. Thanks again everyone!! I will definately post again with my results. P.S. It isn't an indoor pool, we just have the automatic vinyl cover so it keeps it cleaner and safer for the kids. Have a great week.

  6. Back To Top    #6

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Need Help - Chlorine Not Holding

    If you want a rough idea of how much chlorine it will take to clear your pool, you can take a 2 gallon bucket of pool water and see how much chlorine you need to add to it before you get a consistent FC reading. 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC. Add some chlorine, wait about 10 minutes, take a reading, add some more if it's low, repeat.

    Also, I would not trust the pool store numbers. You need to get your own good test kit such as the TF-100 from It will be the best money you have ever spent. You simply cannot properly manage a pool shooting in the dark which is what you do without proper testing and unfortunately many pool stores do not test properly (especially with the CYA test).
    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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