Two Little Fishies Little Reborn Calcium Reactor Media, 4 Kilo, is composed of the fossil skeletons of reef building corals sustainably harvested from pristine sites in the Western Pacific. When used in a calcium reactor, the media will dissolve (at appropriate pH levels), replenishing calcium, carbonate alkalinity, strontium and trace elements. The coarse size of Little ReBorn allows for unrestricted water flow and easy diffusion of carbon dioxide, for maximum efficiency and easy maintenance of the calcium reactor. ReBorn dissolves completely and will not turn to mush! The size of the shells and coral pieces for Little Reborn is slightly smaller then the original version.