Two Little Fishies Strontium Pronto is made from fast-dissolving high purity strontium chloride that provides an easy and economical way to rapidly raise the strontium ion concentration in aquariums. Strontium supplementation is often required in reef aquariums because corals, clams, snails, tube worms, and calcareous algae extract it from the water they deposit calcium carbonate. 250 grams.