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Thread: How much chlorine to overcome demand ?

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    Question How much chlorine to overcome demand ?

    Hello Forum Members !

    I'm new here, and hope to contribute soon but need a little help to get going.

    Most of the summer has been trouble-free, but I went away for a week and came back to a cloudy, out-of-balance pool which I suspected as being in "chlorine-demand" based on previous experience. Test strips were difficult to read.
    I added chlorine until I got a total and residual reading over 5, about 32 gallons of 12.5%, but in a couple of hours it was back to near zero...and I ran out of chlorine on hand
    I will buy a good test kit, but meanwhile took a sample to a Bioguard dealer for computer analysis, results as follows:
    TDS: 2400
    CYA: 30
    TC: 0.6
    FCL 0.3
    PH: <6.6
    TA: 91
    Adj. TA: 82
    Total Hardness: 130

    Water is clear, 82degF. I'm using PhosFree to reduce phosphates. Per the computer analysis recommendations,
    I've added 25 lbs of NaHCO3 to raise alkalinity and am about to add 6 lbs Na2CO3 to raise pH.
    Is there a calculation on this forum of how much chlorine will be needed at this point to correct the pool ?

    Pool store says I need 55 gallons of shock to overcome the demand, but from reading these forums (fora ?) I understand it could be a multi-day process.

    I appreciate your help !
    Thanks !
    OIcu2
    17x50 Vinyl In-ground, 36k gallons

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    duraleigh's Avatar
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    Re: How much chlorine to overcome demand ?

    Welcome to the forum.
    Is there a calculation on this forum of how much chlorine will be needed at this point to correct the pool ?
    Not really. The answer is it takes what it takes and you test the water to see if you have it all out. With our methods, you will not be able to clear the pool using pool store testing unless you run to them 3-4 times daily. Carefully read the SLAM article in Pool School, it will show you the process and you can decide if you want to take over your pool and manage it to your benefit rather than to the benefit of the pool store.

    You didn't ask but phosphates are irrelevant. You also did not need to raise TA, it was fine.

    Right now, you should be testing and raising your pH up into the seven's 7.4 -7.6 is ideal.

    It's a little difficult to absorb but that computer analysis is woefully inadequate to care for your pool.......it's a slick tool that makes you think you are getting good advice. You aren't
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: How much chlorine to overcome demand ?

    Hello oicu, and Welcome to TFP,

    I suspect what has occurred is while you were away an algae bloom began to rear its ugly head because your FC levels dropped too low, and now it keeps dropping because that algae is now consuming all your chlorine.

    The 1st thing you need to do is Buy yourself that good test kit. Either the TF 100 which can be bought from TFTestkits or the Taylor K-2006C which can be bought from many stores online, and at some pool stores too.

    Pool Store testing isn't always accurate and having the proper test kit that will accurately measure the higher FC numbers during the SLAM that you'll need to perform to rid yourself of this issue is a must.


    Until the test kit arrives I recommend you add 1 gallon of Liquid bleach daily (nothing else) to keep the issue from getting any worse and when your test kit arrives run a full set of levels, post them here and we will be able to assist you more from there.

    Here are some links for you to read over that may help explain what has happened and is happening in your pool.

    ABC's of Pool Water Chemistry (It's the place to start learning)http://www.troublefreepool.com/conte...tain-shockingl

    RECOMMENDED LEVELS, SLAM

    Chlorine/CYA CHART

    Together we can get that pool in the best shape it's ever been in so order that test kit, post your full set of results and we'll get started. Have a wonderful day and again, welcome to TFP.
    24' Round x 4.5 ft deep AGP (15,200 Gallons), Vinyl Liner, Hayward Vari Flo XL Sand Filter- (model SP0714T1),
    TFTestkits , PoolMath , Pool School, RECOMMENDED LEVELS, SLAM & the Chlorine/CYA CHART. Support this Site! TFP Totally Rocks.

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    Re: How much chlorine to overcome demand ?

    OK, here we go...
    I've added 1 gallon of bleach 12.5% every day, while continuing the trichlor tablet in the feeder.
    I received the test kit, results as follows:
    Temp: 78
    FC: 0.8
    CC: 0.4
    TC: 1.2
    pH = 7.0 (I had it up to7.4 two days ago...ongoing problem of keeping pH up..base demand test says I need 11 lbs Soda Ash to get it back up)
    TA = 250
    CYA = 35
    CH = 190
    SI = 0.28

    How should I go about correcting my pool ?

    Thanks !
    -OIcu2
    Thanks !
    OIcu2
    17x50 Vinyl In-ground, 36k gallons

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    Re: How much chlorine to overcome demand ?

    How does the water look?

    You need more chlorine and need to follow these recommendations to prevent algae from growing, Chlorine CYA Chart.

    You need to raise the pH a little more. The pucks are lowering the pH and adding CYA to the pool.

    Use 10ml of water when you do the FAS/DPD test for FC, this way the reagents will do more tests and you still have enough accuracy. Each drop will be .5 ppm of FC instead of .2 ppm.

    If the pool is still having problems with holding FC then you need to start the SLAM process, see my signature.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Test Kits . Pool Math . Chlorine/CYA Chart . The SLAM Process

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    Re: How much chlorine to overcome demand ?

    1. stop using trichlor the best thing for you right now.. it is acidic and dropping your PH and adding CYA...
    2. use poolmath to calculate how much chlorine/bleach you will need to keep above 16FC for your CYA level (use CYA of 40 as there is no 35, it goes from 30 to 40)
    3. continue until you pass the SLAM
    4 test as often as 1 hour until your FC is above 16, I would target 20Fc and add when it gets to 16, if you have to leave for work raise to 24fc.

    hope this helps
    Pool: Intex 16x32 15000 gal, 2 speed 340042, Pentair CC320 Filter, CircuPool SJ45 Salt System, Intermatic PE653RC; Hot Tub: 650 Gal SWG Megachlor
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    Re: How much chlorine to overcome demand ?

    Hello OICU2,

    I'm glad to hear you got your kit in. You are well on your way to a crystal clear pool that you'll soon gain the information to be able to independently maintain yourself.

    I confer with the above posts that the removal of the Trichlor puck from your feeder should be the 1st thing you do, and then it's time to get started working to get your pool in excellent condition. Good luck, and Have a wonderful day.
    24' Round x 4.5 ft deep AGP (15,200 Gallons), Vinyl Liner, Hayward Vari Flo XL Sand Filter- (model SP0714T1),
    TFTestkits , PoolMath , Pool School, RECOMMENDED LEVELS, SLAM & the Chlorine/CYA CHART. Support this Site! TFP Totally Rocks.

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