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  1. I’ve been trying to increase the life of my RO membrane. I know that chlorine, and to a lesser extent, chloramine, can attack the membrane that most of us have in our systems. I already have a total chlorine test kit (DPD-4 tablets and a color comparison chart). I wanted something more precise. And, I wanted to know how much of my reading was coming from free chlorine versus chloramine. I decided to buy the HI701 (Free Chlorine) Hanna Checker. After I received it, I tried it out on the water leaving my carbon blocks. I got a zero reading. That got me wondering if I should have bought the HI711 Total Chlorine Checker. After doing a bit of research, I learned that both the HI701 and HI711 are using a modified USEPA 330.5 method (DPD colorimetric method). I also learned that the key difference between the US EPA standard test for free chlorine, which uses DPD-1 and the total chlorine method (DPD-4) is the use of potassium iodide (KI). Apparently, KI reacts with chloramine quite quickly to convert it to free chlorine. I designed a series of experiments to test a theory that I might actually use my DI701 to determine free chlorine and also for total chlorine. I took some tap water that certainly contains free chlorine. Following the instructions in the HI701 kit, I got a reading of 0.45 ppm-Free Chlorine. I recalibrated the instrument and reanalyzed the same sample and got a reading of 1.07 ppm-Free Chlorine. I recalibrated the instrument and repeated the analysis of the same sample three more times and got readings of 1.31, 1.4 and 1.51 ppm-Free Chlorine. It seems that over time, the color got more pink as the readings increased. Perhaps the chloramine was slowly converting to free chlorine. Maybe this is why the Hanna HI701 assay instructions says to mix for 20 seconds and then wait only 1 minute before taking the reading. To the same sample, I added 1 crystal of KI. It got a darker pink in about 10 seconds After 20 seconds I did a series of calibration and sample analysis. My readings were 2.04, 2.13, 2.14 and 2.14. I cleaned out the sample tube with RO/DI water and filled it with fresh tap water. I added 1 DPD-4 tablet from my SpectraPure chlorine test kit. Using the color chart that came with the SpectraPure kit, I gaged the result to be between 2.0 ppm and 3.0 ppm. I placed the sample tube into the HI701 after calibrating it and got a reading of 2.15. I repeated the analysis, calibrating the HI701 each time and got these readings: 2.15, 2.10, 2.05. Seems like the DPD-4 tablet achieves the same result as the HI701 reagent plus some KI added. It also seems to show that the chlorine level is dropping with time as it sits. Perhaps that is why the SpectraPure instructions say to make the reading after the tablet dissolves and before 60 seconds elapses. What I now believe is that one can “qualitatively” do both a free chlorine and total chlorine analysis using the HI701. I do not have access to a reference standard or an instrument that can precisely quantify the level of chloramine in a water sample. The best I can say is that using the Hanna Checker HI701 with DPD-4 tablet from SpectraPure gives a similar reading to using the SpectraPure test kit per instructions. For the same water source, a very similar total chlorine result was obtained by using the Hanna Checker HI701 using its HI701-25 reagent AND adding one small crystal of Potassium Iodide. So, if you are thinking about buying both the HI701 and the HI711 to measure both free chlorine and total chlorine you might be able to use one of them to do the job of both. If you can only buy one, I would recommend the HI711 since it does pick-up both free chlorine and total chlorine. If you get a reading above 0.1 ppm with the HI701, you just won’t know if it is the less harmful (and harder to remove) chloramine, or if it is free chlorine. If you do want to make a more informed analysis of the level of free chlorine AND chloramine, then you might consider doing what I did and purchase the HI701 but add KI to the sample after the first reading (free chlorine) to obtain the total chlorine). You can obtain reagent grade Postassium Iodide from ScienceLab.com, Rocky Mountain Reagents (rmreagents.com) or even ebay. By the way, I did contact Hanna and inquired about my theory. I asked if I could simply use the HI711-25 reagent with the HI701 Checker to obtain total chlorine results. They said I could not do that. Just thought I would provide full disclosure here. I'd welcome any one's insights here. I'll bet folks with swimming pools could shed even more light on what I've seen here.
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