Salifert Magnesium Mg profi testSalifert Magnesium Profi Test Magnesium is present in natural sea water in a fairly high concentration (1350 1500 mg L) and is an essential element of chlorophyll which is necessary for photosynthesis. Without photosynthesis plants, algae and coral would not be able to survive. Magnesium also helps to maintain the correct combination of calcium concentration and alkalinity as it slows down the formation of calcium carbonate which can absorb many