FlexiTester Basic Set Chlor/pH/Alkalinity/Cyanuric Acid (Stabilizer) for semi-professional water analysis. Similar to a pool tester, the FlexiTester involves taking a sample of the water to be measured and adding a tablet that colors the sampled water. Then, a color comparator is inserted, which has a continuous color scale printed on it. The color comparator is moved up and down until the color of the comparator matches that of the colored water sample in the window. Due to the continuous color scale on the comparator, color matching is incredibly easy and significantly more accurate than with conventional pool testers.