The HI-93719-01 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate colorimetric measurements. These reagents follow adaptation of the Standard Methods for the Examination of Water and Wastewater, 18th ed., colorimetric method. The reaction between Mg and calmagite indicator causes a violet tint in the sample. A separate sample is treated with EDTA to chelate all calcium and magnesium present. A separate sample is treated with EDTA to chelate any calcium that is present. The difference in colour of the two treated samples is determined by a compatible benchtop or portable photometer. The concentration of magnesium is displayed in mg/L (ppm) as calcium carbonate (CaCO3). These reagents are designed to be used with samples that have an expected range of 0.00 to 2.00 mg/L magnesium hardness and 0.00 to 4.70 mg/L total hardness.