Figure 4 - This picture shows an injection system using a peristaltic pump. In order to determine the mass of chlorine being added, the user will need to know the flow rate of the irrigation system, the injection rate of the peristaltic pump, and the chlorine concentrate tank below the pump. (Photo Credit: Faith Critzer, Washington State University.)
Most chlorine test kits available on the market will measure total chlorine (HOCl + OCl- + chloramines), free available chlorine (HOCl + OCl-), or only hypochlorous acid (HOCl). Recall that HOCl is the most active form of chlorine and is highly influenced by pH of the water. Overall, there are three types of chlorine measurement devices, including 1) pH and ion specific test strips; 2) colorimeters (titration, spectrophotometric, direct read); and 3) electrodes (ion specific).
Test strips are widely available and are the least expensive option for measuring chlorine concentration. They are user-friendly as operators dip the strip in a water sample for a prescribed length of time, hold for a few seconds, and compare to a color chart for an estimate or range of concentration. It is important to understand what form of chlorine you are testing and be able to test the desired chlorine concentration. In addition, users will need to consider the test strips’ expiration dates. It is important to note that there is variation in methods and procedures used to perform the tests with these strips from brand to brand. Also, there is variability in the color spectrum used to gauge the results of the test.
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