ReBorn Calcium Reactor Media 8.8 lbs. (4 KG), Two Little Fishies. ReBorn coarse aragonite media for calcium reactors, composed of fossil skeletons of reef building corals sustainably harvested from pristine sites in the Western Pacific. When dissolved, ReBorn replenishes calcium and carbonate alkalinity, strontium and trace elements. The coarse size of 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!