Marine aquaria include "fish only" tanks, "fish only with live rock" (FOWLR) tanks, and "reef tanks". Fish only tanks often showcase large or aggressive marine fish species and generally rely on mechanical and chemical filtration. FOWLR and reef tanks use "live rock", a material composed of coral skeletons harboring beneficial nitrogen waste metabolizing bacteria, as a means of more natural biological filtration. A reef aquarium or reef tank is an aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the coral reef environment. A reef aquarium requires appropriately intense lighting, turbulent water movement, and more stable water chemistry than fish-only marine aquaria, and careful consideration is given to which reef animals are appropriate and compatible with each other.

Components

Reef aquariums consist of a number of components, in addition to the livestock, including:

Display tank: The primary tank in which the livestock are kept and shown.

Stand: A stand allows for placement of the display tank at eye level and provides space for storage of the accessory components.

Sump: An accessory tank in which mechanical equipment is kept. A remote sump allows for a clutter-free display tank.

Refugium: An accessory tank dedicated to the cultivation of beneficial macroalgae and microflora/fauna. The refugium and sump are often housed in a single tank with a system of dividers to separate the compartments.

Lighting: Several lighting options are available for the reef-keeper and are tailored to the types of coral kept.

Canopy: The canopy houses the light fixtures and provides access to the tank for feeding and maintenance.

Filtration and water movement: A variety of filtration and water movement strategies are employed in reef aquaria. Bulky equipment is often relegated to the sump.