The HI758U-26 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Marine Calcium Checker® HC. These reagents follow the Zincon Method in which the reaction causes a blue tint in the sample. By simply adding 1 mL of the first reagent to the sample, followed by a packet of the second reagent in the HI758U-26 set, the reaction will take place and the HI758 will determine the concentration from the color that is produced. The results will be displayed in ppm of calcium. These reagents are designed to be used with samples that have an expected range of 200 to 600 ppm calcium.Good for 25 tests