An encrusting form of algae that forms calcareous crusts like coral. Coralline algae is very colorful, occurring in bright purple, pink and red colors. It is very desirable in the reef tank, and can be made to grow on rocks and other hard surfaces by maintaining optimum pH, alkalinity and calcium levels.
Coralline algae are red algae in the Family Corallinaceae of the order Corallinales characterized by a thallus that is hard as a result of calcareous deposits contained within the cell walls. Unattached specimens (maerl, rhodoliths) may form relatively smooth compact balls to warty or fruticose thalli. Many are typically encrusting and rock-like, found in tropical marine waters all over the world.