The HI780-25 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Marine pH Checker® HC. These reagents follow the Phenol Red method in which the reagents produce a range of color that is pH-dependent. By simply adding 5 drops from the bottle of the reagent to the sample, the reaction between the sample and reagent causes a tint in the sample that varies from yellow to red. The intensity of the colour is determined by a compatible photometer and the concentration will be displayed. The results will be displayed in pH units with a resolution of 0.1 pH.