The HI781 Checker®HC (Handheld Colorimeter) is a simple, accurate, and cost-effective way to measure nitrate from 0.00 to 5.00 ppm (as NO3–) in your saltwater aquarium. For samples containing 5.0 to 50.0 ppm nitrate, follow the approved dilution procedure.Nitrate is a by-product of the Nitrogen cycle. Excessive amounts of nitrates in a reef aquarium can promote the growth of undesirable organisms including algae and dinoflagellates while insufficient amounts can lead to starvation in which SPS and other corals will show signs including the loss of color and paleness.The HI781 Nitrate Checker HC is a handheld colorimeter that uses the Beer-Lambert principle to determine the concentration of nitrate colorimetrically. The HI781 is designed specifically to measure low levels of nitrate in a saltwater aquarium.Features at-a-glance: - For use with saltwater samples. - More accurate than chemical test kits. - Dedicated to a single parameter. - Small size, big convenience. - No errors with a digital readout. - Ideal for aquariums and marine biology applications. - For samples containing 5-50 ppm nitrate, follow the dilution procedure.