Nature's Ocean Purple Base Rock 20LBS (Approx. 5 -9 inches) Purple base rock will become naturally live overtime because of its porosity : No artificial or engineered bacteria, Rapidly adapts to the LIVE environment , Made from aragonite base rock, Will not cause pH spikes, Similar in composition to LIVE rock, Perfect for Coral farming, Free of Biofilm, Naturally clean, Helps to conserve Natural reefs, Will not affect the cycling of your tank , Safe for all corals, fish and invertebrates ,and Does not contain glue or cement.