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Thread: free versus total chlorine

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    free versus total chlorine

    Is there an article to explain this concept to me? I have never registered a difference with my test kit b/t free and total, but tonight, there was no free chlorine and a lot of total chlorine. What does this mean? Thanks!

    Erin
    27' AG round pool; vinyl liner; 1 HP pump; 40 GPM Tagleus sand filter

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    Re: free versus total chlorine

    Combined chlorine (CC) is the chlorine in the water that is bound to organics (dirty stuff). Free chlorine (FC) is the available chlorine in your water that is not bound to organics, but is free to disinfect when needed. Your free chlorine and your combined chlorine are added together and the result is your total chlorine (TC).

    So...FC+CC=TC

    If there is no free chlorine but there is lots of total chlorine, this means that your water is dirty and you need to shock. Does this make sense?
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
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    Re: free versus total chlorine

    okay - got it! thanks! I was hoping for a simple answer like that!

    Blessings,

    Erin
    27' AG round pool; vinyl liner; 1 HP pump; 40 GPM Tagleus sand filter

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    Re: free versus total chlorine

    Quote Originally Posted by queenofmyswamp
    okay - got it! thanks! I was hoping for a simple answer like that!

    Blessings,

    Erin
    No problem.
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
    TF Test Kits - Pool Math - Pool School
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    Re: free versus total chlorine

    this morning, still a lot of total chlorine and no free chlorine. I added 4 1-lb bags of di-chlor (almost double the recommended shock amount) and half an hour later, still tons of total but no free registering. Help!! Throwing $20 of shock in there (I'm out of bleach) for nothing is really killing me......
    27' AG round pool; vinyl liner; 1 HP pump; 40 GPM Tagleus sand filter

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    Richard320's Avatar
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    Re: free versus total chlorine

    Quote Originally Posted by queenofmyswamp
    this morning, still a lot of total chlorine and no free chlorine. I added 4 1-lb bags of di-chlor (almost double the recommended shock amount) and half an hour later, still tons of total but no free registering. Help!! Throwing $20 of shock in there (I'm out of bleach) for nothing is really killing me......
    To be sure, now.... You're using the powder and drops?

    It turns Barbie Pink when you add powder. You add drops and swirl until it goes clear. That's FC. Then you add the other drops. Does it turn pink again? If it does, you have CC and you add the 871 again, until it goes clear. That number is CC. Add the two to get TC.

    It's easy to get confused, because the drop-only test is different.

    Edit: I read your post history and see you're using K-2005. Here's how they do it.

    Chlorine (Free, Combined, Total) Test

    1. Rinse and fill small comparator tube to 9 mL mark with
    water to be tested.

    2. Add 5 drops R-0001 and 5 drops R-0002. Cap and invert
    to mix.

    3. Match color with color standard.* Record as parts per
    million (ppm) free chlorine (FC).

    4. Add 5 drops R-0003. Cap and invert to mix.

    5. Match color immediately. Record as ppm total chlorine (TC).

    6. Subtract FC from TC. Record as ppm combined chlorine (CC).
    Formula: TC - FC = CC.

    One test adds numbers, the other subtracts. Be sure you do it right.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
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    Re: free versus total chlorine

    I have the older K-500 test kit, so the DPD only goes up to 5. I add 5 drops of one liquid for free chlorine and 5 drops of something else to get total chlorine. When chlorine levels are really high, I follow the directions for using half pool water and half tap water. I am familiar with the test, so I am fairly confident that isn't the problem. I will say that yesterday morning, we vacuumed the bottom of the pool and got quite a bit of stuff, so I imagine we stirred up a bit of an algae storm in there. I just want to be sure that more and more chlorine is the answer, because the total chlorine is about at a 15 but absolutely no traces of free chlorine. In several years of using this site and having a test kit, I have never had this issue with total and free chlorine, so I am a little out of sorts about it.

    Thanks!
    27' AG round pool; vinyl liner; 1 HP pump; 40 GPM Tagleus sand filter

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    Re: free versus total chlorine

    Okay, here's where I think that you may be getting confused. You are using the little test block that has the chlorine scale on the left and the pH scale on the right, correct? So, when you get your sample, you add 5 drops of the R-0001 and then 5 drops of the R-0002 right? Then cap and invert to mix and take your reading. This reading would give you your free chlorine and not your total chlorine. Then, you add 5 drops of the R-0003 and then cap and invert to mix. Take a reading and this will give you your total chlorine.. Subtract your free chlorine from your total chlorine and that result would be your combined chlorine. It seems that you were thinking that after adding your first two reagents to the sample, you were interpreting that as total chlorine which it is not.

    Another thing about the dilution with half pool water and half tap water. Of course, diluting a sample of anything can get you in the ballpark sometimes but the accuracy really does lack quite a bit. And by diluting with tap water, you also must contend with the extras in the tap water itself that can interfere with results. When diluting a sample, you should only use distilled water. Tap water has TA, calcium, and chlorine in it.

    I am also concerned about your use of dichlor to shock. This adds CYA very quickly to your pool water. The more CYA you have, the more chlorine you will need to sanitize your pool water. This is why we recommend the use of sodium hypochlorite (bleach) for shocking purposes. It doesn't add anything that you don't want in there.

    To be accurate and ensure the best quality in your pool water, you will need to get a better test kit and it needs to be a service level kit that tests for FC, CC, TC, CYA, CH, TA, and pH. I would recommend a TF100 test kit. There is a link in my signature line. This kit has a FAS-DPD chlorine test that is far more accurate than what you have currently and is capable of testing chlorine levels far beyond 5 ppm. This is a necessary thing for you.
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
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    Re: free versus total chlorine

    (hanging head in embarassment)....you are correct - I was taking readings after the first 5 drops and then after the second 5 drops. Guess I need to start over and read the directions each spring. Now I have a pool that is 1/2 bleach and half water. LOL. Thanks for the reminder about the CYA and di-chlor. I actually need to get the CYA level up since we had (have) a leak in the liner so we added about 3 feet of water a few weeks ago and have almost no CYA right now.

    On a side note...what is the significance of the B767 line on your signature? Just curious...
    27' AG round pool; vinyl liner; 1 HP pump; 40 GPM Tagleus sand filter

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    Re: free versus total chlorine

    That's alright. We are here to help you out.

    Unless you fly, that quote probably doesn't make sense. It's a long story but I'll send you a PM if about it if you want. Long story short, when I was working a a nurse on a helicopter, we flew behind a Boeing 767, encountered their wake turbulence, and it was a rough ride to put it mildly.
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
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    Re: free versus total chlorine

    Quote Originally Posted by queenofmyswamp
    Now I have a pool that is 1/2 bleach and half water. LOL.
    So what is your FC/TC now that you are measuring correctly?
    24' x 52" AGP = 13.5k gallons
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    Re: free versus total chlorine

    TC and FC are both holding at about 10 but water is still so cloudy I can't see the second step.
    27' AG round pool; vinyl liner; 1 HP pump; 40 GPM Tagleus sand filter

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    Re: free versus total chlorine

    The cloudy water should begin to clear shortly. Run your filter 24/7 and be sure to backwash when you have a 8-10 pound increase in pressure at the filter. Continue to brush your pool and monitor your FC,CC levels.
    coloeb,
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    Re: free versus total chlorine

    Should I shock my pool if CC is greater than 0.5ppm even if FC is acceptable level? Pool water is clear.
    35K gallon plaster IGP, free form, spa with spill-over; Sta-Rite 2HP pump; KDI American 48sq.ft., 144GPM DE filter; Pentair MiniMax heater; pressure side The PoolCleaner; Circupool RJ45

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    Re: free versus total chlorine

    Yes, though if is just a little higher (say 1.0 or 1.5) you can try simply raising FC up to the high end of the normal range for 24 hours and see if that takes care of it. If CC is higher, or doesn't clear up in 24 hours, you do need to shock.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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