The HI-783 Marine Magnesium Checker provides an accurate way to measure magnesium within saltwater fish tanks. Our digital reef water tester provides clear information about the magnesium levels in your marine aquarium, enabling you to make effective changes to your water quality. Conducting regular aquarium magnesium tests is key to having the information to maintain a healthy tank. As part of the Hanna Checkers range, the HI-783 delivers accurate, fast testing results with no guesswork required.