A reef aquarium or reef tank is a marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the tropical 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. Display tank A "reef ready" or simply "drilled" tank is often used. This style of tank has holes drilled into the rear pane allowing water to drain into the sump or refugium. These drains are usually housed in an internal overflow apparatus made of plastic or glass which encloses a drain standpipe and a water return line. The surface water pours over the overflow, down the standpipe, through PVC piping, into the sump. After transiting the sump, water is pushed by a return water pump through the second hole and into the aquarium. Alternatively, standard non-drilled aquariums employ an external "hang-on" overflow that feeds water via continuous siphon to the sump. The tanks are usually constructed from either glass or acrylic. Acrylic has the advantage of optical clarity, lightness, and ease of drilling. Drawbacks include a tendency to scratch easily, bowing, and often limited access from above due to top bracing. Glass aquariums are heavier but harder to scratch. Other materials such as epoxy-coated plywood have been used by