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Thread: Lower Tot CL than Free CL?

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    Lower Tot CL than Free CL?

    Ok, so I have a question...Today when figuring out our PPM chloramines, we were getting lower Total CL numbers then our Free CL numbers. We use the PalinTest method of testing the water, and nothing has changed. Our Tablets are fresh and good, and 4 out of our 6 pools got the lower numbers. What could possibly cause this? We even re-ran the tests on the pools in question and got the same results. Anyone have any ideas?

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD
    That usually means incorrect test procedure, bad reagents/tablets, or out of calibration meter. I am not familiar enough with PalinTest equipment to know if there are any interferences that could cause that, but none of the systems I am familiar with have such interferences.
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    Are tablets are new, however I suppose there could have been a bad batch or something. The PalinTest method of testing is basically a light photometer, so I suppose is could be out of calibration, as the ambient light cover was on during the test so there really wasn't any interferences. Thanks.

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    It is a DPD test and it is possible that when the chlorine levels are high the test is bleaching out somewhat. For some reason TC can bleach out faster than FC. When this happens it is not uncommon for the TC to measure lower than the FC. I see this at work with our LaMotte colorimeter.

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