These aquarium setups vary from having many fish that vary from chlorinating fish and spawning fish, which attempt to recreate life specific to one region of the world like the Great Barrier Reef, to the more prevalent and often spectacularly colored mixed reef that blend hard and soft corals from around the world.
Regular glass or acrylic style aquariums are used for reef aquariums; these usually include an internal overflow made of plastic or glass which encloses holes that have been drilled into the bottom glass to accommodate a drain or standpipe and a return line (See fig 1, a). Water pours over the overflow into and down the standpipe(See fig 1, b), through PVC piping, into a sump, which generally houses various filtration and heating equipment, through a return water pump and finally back via more piping through the second hole into the aquarium (See fig 1, c). Alternatively, aquariums sometimes employ an external "hang-on" overflow with a U-tube that feeds water via continuous siphon to the sump(See fig 1 d) which returns it via a water pump.
More usual combined mechanical/biological filtration is avoided because these filters trap detritus and produce nitrate which may stunt the growth or even kill many delicate corals. Chemical filtration is used sparingly to avoid discoloration of the water, to remove dissolved matter (organic or otherwise) and to help stabilize the reef system.
"Since flow speed is the critical measure for determining the rate of gas exchange, turnover does little to convey how fast a coral will respire and photosynthesize.
To create turnover many reef aquarists use an Overflow (internal or external) which drains water into a sump where it is then pumped back into the tank. Tanks that come equipped with an internal overflow and pre-drilled holes are known in the hobby as "Reef Ready" or simply "Drilled" tanks. Of the many methods of creating the required flow, one of the most popular is by using multiple powerheads which are simply small submersible water pumps. The pumps may be randomly switched on and off using a wave timer, with each aimed at the flow of another powerhead or at the aquarium glass to create flow in the tank. Another method gaining popularity is the closed loop in which water is pulled from the main tank into a pump which returns the water back into the aquarium via one or more returns to create water turbulence. Only recently available commercially, submersible propeller pumps are gaining popularity due to being able to generate large volume of water flow (turbulent flow) without the intense directed force (laminar flow) of a power head. Propeller pumps are more energy-efficient than powerheads, but require a higher initial investment.
Another recent method is the gyre tank. A gyre tank encourages a maximum amount of water momentum through a divider in the center of the aquarium. The divider leaves an open, unobstructed space which provides a region with little friction against water movement. Building water momentum using a gyre is an efficient method to increase flow, thus benefiting coral respiration and photosynthesis.
Water flow is important to bring food to corals, since no coral fully relies on photosynthesis for food. Gas exchange occurs as water flows over a coral, bringing oxygen and removing gasses and shedding material. Water flow assists in reducing the risk of thermal shock and damage by reducing the coral's surface temperature. The surface temperature of a coral living near the water's surface can be significantly higher than the surrounding water due to infrared radiation.
Many, if not most aquarium corals contain within their tissue the symbiotic algae called zooxanthellae. It is these zooxanthellae that require light to perform photosynthesis and in turn produce simple sugars that the corals utilize for food. The challenge for the hobbyist is to provide enough light to allow photosynthesis to maintain a thriving population of zooxanthellae in a coral tissue. Though this may seem simple enough, in reality this can prove to be a very complex task.
Some corals such as the Mushroom Coral and Coral Polyps require very little light to thrive – conversely, LPS coral such as Brain coral, Bubble Coral, Elegance Coral, Cup Coral, Torch Coral, and Trumpet Coral reqiure moderate amounts of light, and Small Polyp Stony Corals (SPS) such as Acropora Coral, Montipora, Porites, Stylopora and pocillopora require high intensity lighting.
Of the various types, most popular aquarium lighting comes from metal halide, very high output or VHO, compact fluorescent and T5 high output lighting systems. Although they were once widely used, many reef tank aquarists have abandoned T12 and T8 fluorescent lamps due to their poor intensity, and mercury vapor due to its production of a limited light spectrum.
Recent advances in lighting technology have also made available a completely new technology for aquarium lighting: lightemitting diodes (LEDs). Although LEDs themselves are not new, the technology has only recently been adapted to produce systems with qualities that allow them to be considered viable alternatives to gas- and filament-based aquarium lighting systems. The newness of the technology does cause them to be relatively expensive, but these systems bring several advantages over traditional lighting. Although their initial cost is much higher, they tend to be economical in the long run because they consume less power and have far longer lifespans than other systems. Also, because LED systems are comprised of hundreds of very small bulbs, their output can be controlled by a microcomputer to simulate daybreak and sunset. Some systems also have the ability to simulate moonlight and the phases of the moon, as well as vary the color temperature of the light produced.
The choices for aquarium lighting are made complicated by variables such as color temperature, (measured in kelvins), color rendering index (CRI), photosynthetically active radiation (PAR) and lumens. Power output available to the hobbyist can range from a meager 9 W fluorescent lamp to a blinding 1000 W metal halide. Lighting systems also vary in the light output produced by each bulb type--listed in order of weakest to strongest they would be: T8/12 or normal output lamps, compact fluorescent and T5 high output, VHO, and metal halide lamps. To further complicate matters, there are several types of ballasts available: electric ballast, magnetic ballast, and pulse start ballast.
Luckily, the choice of lighting systems for a hobbyist can usually be narrowed by first determining which types of corals the hobbyist plans on keeping, since this is the primary factor in determining lighting needs.
Most hobbyists agree that a reef tank should be kept at a temperature between 25 and 27 °C (75-80 ºF). Radical temperature shifts should be avoided as these can be particularly harmful to reef invertebrates and fish. Depending on the location of the tank and the conditions therein (i.e. heat/air conditioning), you may need to install a heater and/or a chiller for the tank. Heaters are relatively inexpensive and readily available at any local fish store. Aquarists frequently use the sump to hide unsightly equipment such as heaters. Chillers, on the other hand are expensive and are more difficult to locate. For many aquarists, installing surface fans and running home air conditioning suffice in the place of a chiller. Fans cool the tank via evaporative cooling and will require more frequent top off of the aquarium.
Nano reefs also require extra care in the selection of occupants. There are two major factors to be considered: biological load, i.e. the ability of the tank to process the wastes produced by the occupants, and species compatibility. These issues, though present in larger tanks, are magnified in the nano tank. Species considered reef safe and able to coexist in larger tanks may not do well in a nano tank due to their close physical proximity. For this reason, smaller species of fish such as gobies and clownfish are popular choices due to their relatively small size and ability to coexist peacefully with other tank inhabitants.
However, it is largely recommended that nano reef aquarists use devices such as protein skimmers to remove excess wastes from the aquarium Before it has a chance to be broken down in to nitrate.