The Salifert Magnesium Test Kit measures the magnesium content in saltwater aquariums. In nature, magnesium is present in rather high concentrations such as 1300 - 1400 mg/L, and contributes heavily to photosynthesis, a process that sharply determines the growth and health of aquatic plants, algae and corals. Magnesium plays an important role in the aquarium environment. It controls and maintains the optimal balance of calcium concentration and alkalinity to ensure that the necessary and important calcium carbonates are formed naturally and not through undue chemical processes. The calcium carbonates contribute to the growth and development of corals and beneficial algae. The Salifert Magnesium Test Kit measures the amount of magnesium incrementally by 30 mg/L.