JBL MagesiuMarin is a magnesium supplement for the professional care for the reef aquarium. The Popular calciferous red algae and invertebrates that develop a calcareous skeleton or a hard shell in reef aquariums need sufficient magnesium to build up their shells or skeletons. Possible consequences of inadequate magnesium content are defective growth in rock corals and calciferous red algae and insufficient skeletal development in echinoderms and moulting problems in crustacean.