the appearance and the health of the tank. The sump helps the appearance of the tank, because it allows filtration and maintenance equipment (protein skimmer, heater, activated carbon) to be kept out of sight of the main tank. It also ensures that the water level of the main aquarium never changes, as the overflow sets the water level in the main tank. The sump aids tank health by helping to oxygenate the water by increasing the amount of water/air surface area used for gas exchange. Some marine aquariums also include a refugium. Refugiums are small containers or aquariums that are hidden behind or beneath the main aquarium and connected to it via a water pump (often in a similar manner to a sump). Refugiums have recently become quite popular among reef aquarists because they can be used to serve several purposes such as adding water volume or providing a fish-free site for biological filtration in live rock and/or the sandbed. Fish-free refugiums host populations of copepods, amphipods, isopods, and other zooplankton. Lighting Regular cyclical lighting is used in aquariums to simulate day and night. This is beneficial for fish and invertebrates since it establishes a routine, enables them to rest, and makes them feel more secure. Aside from establishing a routine, high output lighting is required for many invertebrates such as corals and anemones to survive. Lighting in marine tanks that contain only fish and live rock is not an important issue. In marine aquariums containing corals, or other photosynthetic invertebrates, where algal growth (of both free-living and symbiotic algae) is desired, more intense lighting is required. Since the intensity of the light will vary based on the source and distance from the source, lighting requirements are sometimes described using a measurement called Photosynthetically Available Radiation, or PAR. Various light sources include but are not limited to: natural sunlight, fluorescent, VHO fluorescent (Very High Output), T-5 fluorescent, compact fluorescent, LED and metal halide. Each type of lighting has its own advantages and disadvantages. They all vary in initial cost, maintenance cost, spectrum obtainable, longevity, efficiency, and power. Natural sunlight The most primitive lighting source is natural sunlight. This is only effective in areas near the equator because the intensity of sunlight is greatest there. Efficiently utilizing natural sunlight requires complex planning and, as such, this method is applied on only the largest reef systems. Many times in the hobby natural