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Thread: Why isn't my TC higher than FC?

  1. Back To Top    #1

    Join Date
    Jul 2009
    El Paso, TX

    Why isn't my TC higher than FC?

    My pool was cloudy yesterday and the total chlorine (TC) and the FC was 0. Here are the readings from yesterday from the pool store.

    CH 240
    TC 0
    FC 0
    pH 7.3
    TA 150
    CYA 70

    I figured that the water was cloudy because I was getting algea. So I added 4 gallons of 6% bleach last night and another 2 gallons this morning. I rechecked the water with an Aquachem test strip this morning. This is what I got:

    CH 250
    TC 3
    FC 3
    pH 7.8
    TA 120
    CYA 100

    I aerated it all night by leaving the jacuzzi on. Now I will add a quart of muriatic acid. (Correct?)

    Here is my question: Why is the TC and FC the same? I figured that the TC would be a lot higher than the FC because it would consist of the FC and CC's (chlorine bound to organic material like algea/bacteria). Is this incorrect? If so, can you explain why they are the same? Does the CC's just dissipate into the air or what happens to it?
    1) 20000 gal
    2) DE filter
    3) In Ground
    4) Plaster

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: Why isn't my TC higher than FC?

    CC is zero. CC is often zero. Chlorine and sunlight break down CC. CC can also sometimes evaporate away.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Why isn't my TC higher than FC?

    Welcome to the forum. You may well have CC's but the two testing methods you used are easily the most innaccurate available. Test strips are virtually worthless (I didn't know they even test for CC's) and pool store testing is frequently (but not always) just as bad.

    To get valid results you need to do your own testing with an accurate kit.

    The muriatic addition is good if you believe the strips.....bad if you believe the pool store. I would not add the muriatic until I had an indicator which one was correct (altho, based on your other numbers, it's likely the strips that are closest)

    I would not aerate....that can come much later after you get rid of your algae.

    You do have algae. (even if you have no CC's) Your chlorine consumption shows us that. Read "How to shock your Pool" up in Pool School.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  4. Back To Top    #4

    Join Date
    Jun 2009
    Henderson, KY

    Re: Why isn't my TC higher than FC?

    I'll try to help here. If I'm incorrect, someone with more knowlege can jump in.

    Total Chlorine is just as it sounds; the total amount of chlorine that's in the pool. This includes Free chlorine, which is chlorine that is still active and able to do it's job of sanitizing, and combined chlorine; the chlorine that has been used up doing it's job and has binded with algae and bacteria in the pool. Lets say we start with a FC of 3.0 and a CC of 0.0. Your total TC is now also 3.0. As the free chlorine becomes combined chlorine, you still have a total chlorine of 3.0, but, as the CC starts to rise, the FC starts to drop. If your CC is now 1.5, your FC will be 1.5, still giving you a total chlorine reading of 3.0.

    Any help? Or, clear as mud?

    24' X 52" Vogue Impact AGP - 13,500 gal. (Installed 2001) - Jacuzzi Laser 225 sand filter w/7 way valve, 1-1/2 hp pump - "The Step" single center rail steps - "Zoomerang" deck mounted AG slide w/adjustable water flow - "Aqualuminator" return fitting pool light w/fountain attachment
    Taylor 2005 Test Kit w/add-on FAS chlorine test kit

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