Small Polyp Stony (SPS) Corals are the builders of calcium carbonate reef structures found in the wild. The skeleton of these corals is slowly secreted by the epidermis at the base of each coral polyp. The rate that this occurs depends on the species. Some varieties of SPS corals can grow very quickly while some other varieties take seemingly forever to show any growth. Stony Corals benefit from clean water and a consistent source of calcium, alkalinity, and magnesium.