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Thread: Cl levels not rising to expected levels when adding liquid.

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    Cl levels not rising to expected levels when adding liquid.

    I've been using a combination of liquid chlorine (12.5%) and trichlor tablets for almost a year now. Starting a few days ago, I noticed that the chlorine was not rising to the expected levels when adding liquid chlorine. In other words, shortly after sunset, I'll add an amount of liquid chlorine that should bring up the total chlorine up by 1 ppm. When I check the levels the next morning (or later that night after the pump has been running a few hours), the chlorine levels only show a rise of about 0.4 ppm, less than half of what I expect to see based on my experience over the past year.

    I'm using the same volume for my calculations that I've always used, and am measuring with a Taylor K-2006 kit using the .2 ppm accuracy test. I also checked the CYA, and it looks like it's down around 60 or a bit higher, so I don't see how this could be due to "chlorine lock." I'm also seeing zero combined chlorine in my tests, but is it possible to have high chlorine usage WITHOUT tests showing any CC? I would think that I would see at least SOME CC in my tests. It also seems like if the Cl was being used up at such a high rate, it would be zero by the next morning, but it is not. It seems like it's just lower to start with (after adding it), but that it's dropping at a relatively normal rate. Note that through all this, the water has never looked cloudy -- if it wasn't for the measurements there would be no indication of any problem.

    The only thing that changed recently was that this is a new batch of chlorine. It's Hasa, which I would think would be as good as any, but is it possible to get a bad batch of chlorine? The measurements are behaving like the chlorine is only half as concentrated as it should be.

    Thanks,

    Larry
    Los Angeles, CA -- 22K gallon in-ground plaster pool with spa, built around 1980, replastered around 2009-2010.
    Pentair Intelliflo VS (variable speed) pump and Quad 100 DE filter. Older "MiniMax" gas heater. Pentair Rebel cleaner.
    NO SWG - Liquid Cl only. Taylor K-2006 test kit.

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    duraleigh's Avatar
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    Re: Cl levels not rising to expected levels when adding liqu

    Hey, Larry,

    It is possible to get a weakened batch of chlorine it has a shelf life that isn't great....especially if you are using 10-12%

    And yes, it is possible to have chlorine loss without any CC's.

    When you take these tests, do you have pucks in the water?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Cl levels not rising to expected levels when adding liqu

    If the chlorine is being used up due to contaminants, why wouldn't it show up as CC, especially if the rate of Cl usage is so high? Where does the "used Cl" go if it's not showing up as CC?

    I took the floating puck feeder out of the pool so I can get more accurate tests tonight.

    Thanks for the feedback,

    Larry
    Los Angeles, CA -- 22K gallon in-ground plaster pool with spa, built around 1980, replastered around 2009-2010.
    Pentair Intelliflo VS (variable speed) pump and Quad 100 DE filter. Older "MiniMax" gas heater. Pentair Rebel cleaner.
    NO SWG - Liquid Cl only. Taylor K-2006 test kit.

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    linen's Avatar
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    Twin Cities, MN
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    Re: Cl levels not rising to expected levels when adding liqu

    Quote Originally Posted by lalittle
    If the chlorine is being used up due to contaminants, why wouldn't it show up as CC, especially if the rate of Cl usage is so high? Where does the "used Cl" go if it's not showing up as CC?
    In the process of breaking down organic contaminates (such as algae) one of the by products is CC, which in turn is also broken down by chlorine. It is not uncommon for the chlorine to break down the CC at rate that keeps up with the creation of the CC.

    Quote Originally Posted by lalittle
    I took the floating puck feeder out of the pool so I can get more accurate tests tonight.
    If you are going to do a overnight chlorine lost test (OCLT) make sure to follow our procedure to ensure you get accurate results: http://www.troublefreepool.com/pool-...rnight_fc_test
    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: Cl levels not rising to expected levels when adding liqu

    It turns out that it was indeed a bad batch of chlorine.

    I bought some more chlorine (same brand, different lot number), and this time, the FC levels rose by the expected amount when I added it to the pool.

    I was able to exchange it for another batch.

    Thanks,

    Larry
    Los Angeles, CA -- 22K gallon in-ground plaster pool with spa, built around 1980, replastered around 2009-2010.
    Pentair Intelliflo VS (variable speed) pump and Quad 100 DE filter. Older "MiniMax" gas heater. Pentair Rebel cleaner.
    NO SWG - Liquid Cl only. Taylor K-2006 test kit.

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