The HI719-25 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Magnesium Hardness Checker^® HC. These reagents follow the EDTA colorimetric method in which the reaction between magnesium and the reagent causes a violet tint in the sample. When the HI719-25 reagents are added to the sample, the reaction will take place and the HI719 will determine the concentration from the color that is produced. The results will be displayed in ppm of magnesium hardness as CaCO₃. These reagents are designed to be used with samples that have an expected range of 0.00 to 2.00 ppm CaCO₃.