Since magnesium is a component of the pigment chlorphyll, it is required for all pigmented algae. Magnesium is also required for the formation of the enzyme catalase (Round, 1965), which serves the protective function of breaking down hydrogen peroxide into oxygen and water. Magnesium is unlikely to be a factor limiting the growth of algae in seawater aquariums due to its high concentration in seawater.
A possible exception to this regards the use of magnesium by coralline algae, which deposit it along with calcium carbonate in their skeletons in the form of calcite. Coralline algae skeletons contain from 7 to 30% magnesium carbonate. There are anecdotal reports of die off of coralline algae due to magnesium levels in the aquarium being well below natural seawater values (about 1300 ppm at a specific gravity of 1.025). IT IS IMPORTANT TO REMEMBER THAT NATURAL SEAWATER VALUES ARE MEASURED AT A SPECIFIC GRAVITY OF 1.025. AQUARIST WITH LOW SPECIFIC GRAVITY IN THE AQUARIUM OFTER ERRONEOUSLY BELIEVE THE MAGNESIUM LEVEL IS LOW WHEN IT REALLY ISN'T. At a specific gravity lower than natural seawater, the magnesium concentration will be proprtionately lower than 1300 ppm, and this is not a sign of deficiency.
A possible exception to this regards the use of magnesium by coralline algae, which deposit it along with calcium carbonate in their skeletons in the form of calcite. Coralline algae skeletons contain from 7 to 30% magnesium carbonate. There are anecdotal reports of die off of coralline algae due to magnesium levels in the aquarium being well below natural seawater values (about 1300 ppm at a specific gravity of 1.025). IT IS IMPORTANT TO REMEMBER THAT NATURAL SEAWATER VALUES ARE MEASURED AT A SPECIFIC GRAVITY OF 1.025. AQUARIST WITH LOW SPECIFIC GRAVITY IN THE AQUARIUM OFTER ERRONEOUSLY BELIEVE THE MAGNESIUM LEVEL IS LOW WHEN IT REALLY ISN'T. At a specific gravity lower than natural seawater, the magnesium concentration will be proprtionately lower than 1300 ppm, and this is not a sign of deficiency.
