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Thread: Difference between free and total cholorine

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    Default Difference between free and total cholorine

    Hello all, I've been reading the forum for a couple weeks now and I'm gaining tons of useful information. I'm wondering if somebody can clear up for me the difference between free and total chlorine.

    My pool is approx 14,000 gallons. I should mention that I opened my pool a week ago to find that there is a crack in the intake line buried under concrete that is still in the process of being fixed. So, no filter plus 90 degree heat is not good. But I have been adding chemicals and getting a current going manually in the evenings. Last night free chlorine was pretty much at 0. PH was around 7.2-7.5. CYA 30-50. Alkalinity 80. So I hit it with 3/4 of a gallon of 6% bleach.

    2 hours later the free chlorine was at 0 still with the rest of the numbers holding about the same. I couldn't understand why the FC didnt go up at all. So, I tried another cheap test kit I had and the chlorine was showing 5-10 ppm. What I didn' t realize was this was measuring total chlorine as opposed to free chlorine the other test kit was measuring. In fact until last night I didnt even know there was a difference.

    Today the pH is down to around 7.0. Free Chlorine is still 0. Total chlorine is now down to around 2-4ppm and I'm starting to see a tad bit of the yellow mustard algae show up on the sides of the pool.

    So, whats the difference between the 2? Why is one higher then the other? And what do I need to do to get things where they need to be?

  2. #2
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    Watermom is offline Super Moderator Quark Inspector Watermom 4 stars Watermom 4 stars Watermom 4 stars Watermom 4 stars Watermom 4 stars Watermom 4 stars
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    Default Re: Difference between free and total cholorine

    FC + CC = TC. The very simplistic answer is that free chlorine is the chlorine that is still available to sanitize your water. Combined chlorine is the chlorine that has "already been used up" sanitizing your water and total chlorine is the sum of the two.

  3. #3
    aylad is offline SuperMod Emeritus Vortex Adjuster aylad 4 stars aylad 4 stars aylad 4 stars aylad 4 stars aylad 4 stars aylad 4 stars
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    Default Re: Difference between free and total cholorine

    To get your numbers where they need to be, you need to shock the pool (see the link to the best guess chart in our sigs) and hold it at shock level til your CC goes to zero and your FC starts to hold.

    Janet
    Janet

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