Reef Disks are perfect for the propagation or fragging of hard and soft corals such as Acropora, Birdsnest, Montipora, Kenya Trees, Xenia, zoanthids, ect. They are bright white in color, measure 1.5" wide and 3/8" thick. They are made from 100% Pure Caribsea reef sand. This sand is a natural calcium based sand which has been shown to speed the spread of coralline algae growth and corals on the disks.