A reef tank is a saltwater aquarium dedicated to hosting animals that reside on a typical coral reef. Most commonly this is a mixture of species of coral, clam and invertebrates captured from the wild in areas such as Fiji, Philippines and other tropical islands. More recently a variety of animals is becoming available that are farmed by aquaculture. Usually there are also a variety of fish that are considered reef safe, i.e. do little to no damage to the typical species of animals in a reef tank.

The reef tank setup consists of the basic tank, along with strong lighting and filtration equipment.

Lighting

Most species of coral and clams that are kept in a reef tank are photosynthetic in that they acquire a large portion (up to 95% is typical) of their nutrition from light. In the wild, sunlight is plentiful and of the correct spectrum for optimum health and growth. In captivity, only the largest public aquariums can afford the setups that allow natural light to fill the tank in sufficient quantity to keep the animals alive. Most of the hobby relies on Metal Halide or various fluorescent lighting. A typical 180 gallon reef tank would consist of two 250 watt Metal halide lamps, or four 110 watt VHO fluorescent lamps. This would be considered average lighting, and many people would put 800 watts of metal halide or more over the same sized tank. Most reef tanks have about 5-8 watts of lighting per gallon. Compact fluorescent lamps are also used, but they often don't have the power to light deeper tanks, and the choices of color temperature are not as large as with VHO (very high output) lamps. Fluorescent lamps of the type "actinic" are also used in combination with the Metal Halide lights. The actinic lights produce a blue light and simulate the light reaching the deeper parts of a natural reef. The actinic lights give the appearance of a "black light" - casting a blueish light on everything. Typically they are kept on much longer time periods than the metal halides. A 90 gallon reef setup might have the actinics on for 12 hours per day, whereas the metal halides would only be on for 4 to 6 hours per day in the evening. A good dawn to dusk effect is to keep the actinics on from 10:00 am to 10:00 pm, and the metal halides on from 3:00 pm to 9:00 pm.

Filtration

Filtration is needed to remove accumulated waste from the tank, and supplement materials that the animals use to grow, such as calcium and iodine. Basic filtration is most often achieved with a particle filter of some kind, and a protein skimmer. The particle filter must be cleaned regularly to prevent the accumulated debris from breaking down and further fouling the system. The protein skimmer is very useful in removing certain organics from the water, and as a side benefit helps to aerate the water. A calcium reactor of some kind would also greatly benefit the health of the corals and clams contained within the reef. These animals use the calcium to grow.

Live Rock / Live Sand

Filtration is accomplished naturally via "live rock" positioned in the reef tank. The rock provides the proper substrate for the bacteria to grow to breakdown the waste products produced by the tank inhabitants. The "live sand" or Berlin method can be used in conjunction with the live rock. Here a bed of sand covers the bottom of the tank to provide an area deep within the sand where anaerobic bacteria can complete the final breakdown of wastes.

See also: nano reef