HI7214-25 Pool Line Free Iron Checker HC Reagents are high-quality reagents that are pre-measured, allowing users to achieve fast and accurate measurements with the HI7214 High Range Iron Checker HC. These reagents follow the Phenanthroline Method in which the reaction between iron and reagent causes an orange tint in the sample. By simply adding the packet of HI7214-25 reagent to the sample, the reaction will take place and the HI7214 will determine the concentration from the color that is produced. The results will be displayed in ppm (mg/L) of iron. HI7214-25 Pool Line Iron Checker HC Reagents are designed to be used when measuring swimming pool, hot tub, or spa water that has an expected range of 0.00 to 5.00 ppm iron.