Alkalinity The HI-755-26 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Marine Alkalinity Checker® HC. These reagents follow the Colorimetric Method in which the reaction causes a distinctive range of colours from yellow to green to blue to develop. By simply adding the solution of HI-755-26 to the sample, the reaction will take place and the Marine Alkalinity Checkers will determine the concentration from the colour that is produced. The results will be displayed in ppm of CaCO₃. These reagents are designed to be used with samples that have an expected range of 0 to 300 ppm CaCO₃.   Calcium The HI-758-26 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 HI-758-26 set, the reaction will take place and the HI-758 will determine the concentration from the colour 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.   Nitrate HI-781-25 Marine Low Range Nitrate reagents, 25 tests, for use with the HI-781 Nitrate Handheld Colorimeter Checker.  Uses the Zinc reduction method.   PH The HI-780-25 is the replacement reagents for the HI-780 Marine pH Checker® HC. These high-quality reagents are clearly marked with the lot number and expiry date on the dropper bottle for traceability.   Phosphate The HI-774-25 are high-quality reagents that are pre-measured, allowing for users to achieve fast and accurate measurements with their Phosphate Ultra Low Range Checker® HC. These reagents follow the Ascorbic Acid Method in which the reaction between phosphate and reagents causes a blue tint in the sample. By simply adding the packet of HI-774-25 reagent to the sample, the reaction will take place and the HI-774 will determine the concentration from the colour that is produced. The results will be displayed in ppb of phosphate. These reagents are designed to be used with samples that have an expected range of 0.00 to 0.90 ppm phosphate.