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Thread: high FC -- how do I measure CC?

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    high FC -- how do I measure CC?

    If a deluxe homeowner test kit can't measure chlorine above 5 ppm how can you compute combined chlorine? If the FC is at the top of the scale so will TC. So I will not be able to get a meaningful CC reading.

    This summer the chlorine has been pegged for days on end. I've been adding a 3" tab every day or two to the skimmer (let's not debate that now) to avoid last year's algae crisis.

    Algae has been in check despite the heavy rains in the last month.

    But I smell chloramides when I have my nose near the water. Yet there is no meaningful way to know how much shock to add or even if I should shock considering the apparent high chlorine level.

    The pool store can't measure beyond 5 ppm either and half the answers I get there even I can identify as bogus.

    What would you do short of buying a laboratory quality test kit? Or do I just shock the pool anyway with a standard dose?

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    Mod Squad zea3's Avatar
    Join Date
    Jul 2009
    Houston, Texas

    Re: high FC -- how do I measure CC?

    Hi, welcome to TFP! What you need is the FAS-DPD kit. You can purchase just that test from TF Testkits. The FAS-DPD kit can test FC levels from .2 to over 50 ppm. It will also test the CCs.
    TFP Moderator
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    Re: high FC -- how do I measure CC?

    Thanks I'll hunt for that today. But until that arrives, would you shock? Would like to maintain a swimable pool for the weekend.

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    linen's Avatar
    Join Date
    Jul 2010
    Twin Cities, MN

    Re: high FC -- how do I measure CC?

    Quote Originally Posted by flw
    Thanks I'll hunt for that today. But until that arrives, would you shock? Would like to maintain a swimable pool for the weekend.
    If you can smell the CC's you need to shock. Have you looked at the shocking process?

    You will need to know your cya level (which may be high due to your use of the pucks). When you have that, then you can determine your shock FC level (see: While you are waiting for your kit (and if you feel you have a good number for cya), you can at least maintain your shock level by doing a dilution with your current kit by adding using 1 part pool water and 3 parts non-chlorinated water and multiply your result by 4. This will let you measure up to ~ 20 ppm (although it will not be accurate and you will not be able to do a Overnight Chlorine Loss Test (OCLT) very well).
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: high FC -- how do I measure CC?

    The CYN is a little confusing. As many trichlor tabs as I have used this summer you'd think the CYN would be high. But the test strips show it in the low normal zone. If contaminants are eating the CYN you'd think I could not keep chlorine in the pool. I guess I can see what Leslie's will give for a second opinion.

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    Swampwoman's Avatar
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    Apr 2012
    Grand Rapids, MI

    Re: high FC -- how do I measure CC?

    Contaminants don't eat CYA. It can only leave the water via splash out (or an EXCEPTIONALLY rare form of bacteria that converts it to ammonia, I believe).
    The real test is tricky enough -- I wouldn't trust test strips OR Leslies on it.
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    Re: high FC -- how do I measure CC?

    Thanks for the expertise. Will get much easier with the right kit I'm sure.

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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: high FC -- how do I measure CC?

    If you do not have a CYA test besides the strips (no good) and you need the FAS-DPD test, you are probably best served by ordering one of the full test kits (K-2006 or the better value TF-100).

    CYA is an important number and given your use of tablets ... a value you need to know and be able to test for to make sure it does not get too high.
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