The HI735-25 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Total Hardness Low Range Checker – Checker HC. These reagents follow the DPD Method in which the reaction between chlorine and reagent causes a red-violet tint in the sample. By simply adding the packet of HI735-25 reagent to the sample, the reaction will take place and the HI735 will determine the concentration from the color that is produced. The results will be displayed in ppm (mg/L). These reagents are designed to be used with samples that have an expected range of 0 to 350 ppm (mg/L) as CaCO3.