The HI783-25 are high-quality pre-measured reagents, allowing users to achieve fast and accurate measurements with their Marine Magnesium Checker® HC. These reagents follow the colorimetric EDTA method using calmagite indicator in which the reaction between magnesium and the reagent causes a blue to violet tint in the sample. By simply adding the packet of HI783-25 reagent to the sample, the reaction will take place and the HI783 will determine the concentration from the color produced. The results will be displayed in ppm of Magnesium. These reagents are designed to be used with saltwater samples with an expected range of 1,000 to 1,800 ppm.