The HI774-25 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Phosphate Ultra Low Range CheckerHC. 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 HI774-25 reagent to the sample, the reaction will take place and the HI774 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 of0.00 to 0.90 ppm phosphate.