Magnesium is present in NSW in a fairly high concentration (1300 - 1400 mg/L). Magnesium is an essential part of chlorophyll, which is necessary for photosynthesis. Without photosynthesis plants, including algae and the corals, which we usually have in our aquariums, would not be able to live. Magnesium has another important function since in fact makes maintaining the correct combination of calcium concentration and alkalinity or carbonate hardness possible.
Salifert Test Kit Magnesium