The HI781 Marine Nitrate Low Range Colorimeter is designed to accurately determine low range nitrate levels in saltwater aquariums and marine applications. With a digital read out, there is no more struggling to determine colors visually. - Range: 0.00 to 5.00 ppm (as NO3–) [0.0 to 50.0 ppm (calculated) using dilution] - Built-in timer so you don't miss a step. - Saltwater Compatible