The HI93735-0 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate colorimetric measurements. These reagents follow the EPA recommended method 130.1 in which the reaction between calcium, magnesium, and the reagents causes a red-violet tint in the sample. Depending on the range of the sample, one of three bottles of reagent A will be used, while reagent B and C are used for all ranges. By simply adding the range-appropriate bottle of liquid reagent A, two drops of reagent B, and the packet of reagent C to the sample, the reaction between calcium and magnesium and the reagents causes a color change dependent upon concentration. The intensity of color is determined by the compatible HI97735 photometer and the concentration will be displayed. The results will be displayed in mg/L (ppm) as CaCO3. These reagents are designed to be used with samples that have an expected range of 0 to 250 mg/L, 200 to 500 mg/L, or 400 to 750 mg/L as CaCO3 total hardness.