API Marine Magnesium Raises Magnesium Levels in Reef AquariumsAPI Marine Magnesium Raises Magnesium Levels in Reef Aquariums raises and restores magnesium levels in your reef aquarium, and should be used whenever a magnesium deficiency is present in your water. The magnesium level of a reef aquarium should be between 1,250 to 1,450 ppm. Use API Marine Magnesium when water tests show a magnesium level below 1,250 ppm mg L in your reef aquarium. Dose according to directions on the product label. Treats up to 948