The HI736-25 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Phosphorus Ultra Low Range Checker HC. These reagents follow the Ascorbic Acid Method in which the reaction between phosphorus and reagents causes a blue tint in the sample. By simply adding the packet of HI736-25 reagent to the sample, the reaction will take place and the HI736 will determine the concentration from the color that is produced. The results will be displayed in ppb of phosphorus. These reagents are designed to be used with samples that have an expected range of 0 to 200 ppb phosphorus.