LifeRock Dry Live Rock is infused with spored bacteria to aid in biological performance, featuring millions of micro and macro passageways, making it perfect for environmentally friendly aquarists. It creates a mature-looking reef instantly, is 100% safe for all marine animals, and consists of unique pieces. Made of aragonitic base rock instead of typical cement, it does not affect natural resources and is ideal for marine fish, invertebrates, and corals. The rocks come with an artificial coating that mimics natural coralline algae, with an average of 5-7 pieces per 20 pounds, ranging in size from 8 to 14 inches in diameter.