Nitrate Checker for Saltwater. Measure nitrate in saltwater. The concentration of the nitrate (amount of nitrate) can be easily operated with a single button. digital display. Safe for beginners. HI 782 can measure high concentration range (0.0 - 75.0 ppm) (Uses separate reagents for measurements) Compared to the siblings HI 781 (for low concentration), it is also useful for aquarium (saltwater aquarium), as well as for aquarium cultivation. Recommended for those who use a simple reagent kit that can see the color.