Strontium is used by corals in the same way as calcium and is of equal importance in maintaining vigorous growth. It is especially useful in densely populated aquariums requiring a continuous supply of strontium. Reef Advantage Strontium is a highly concentrated (30,000 ppm) ionic strontium supplement. Unlike other strontium chloride products, Reef Advantage Strontium is formulated so that it can be added directly to the aquarium. 250 ml treats 4000 l.