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See also: Marine aquarium.

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.


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 TankEdit

Main article: Aquarium

A "reef ready" or simply "drilled" tank is often used. This style of tank has holes drilled into the bottom pane allowing water to drain into the sump or refugium. These drains are usually housed in an internal overflow aparatus made of plastic or glass which encloses a drain standpipe and a water return line (See fig 1, a). The surface water pours over the overflow, down the standpipe (See fig 1, b), through PVC piping, into a sump. After transiting the sump, water is pushed by a return water pump through the second hole and into the aquarium (See fig 1, c). Alternatively, standard non-drilled aquariums employ an external "hang-on" overflow that feeds water via continuous siphon to the sump (See fig 1 d). 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 industrious DIY'ers.


Main article: Filter (aquarium)

The primary filtration for reef aquariums usually comes from the use of large amounts of live rock which come from various rubble zones around existing reefs or more recently aquacultured rock from Florida[1]. Deep sand beds[2] (DSB) are often employed to augment this biological filtration. Deep sand bed opponents may prefer a "bare bottom" or "suspended reef" which allows for easier removal of accumulated detritus. This biologic filtration is usually supplemented by protein skimmers. Protein skimmers use the foam fractionation process wherein air is introduced into a water stream creating microbubbles. Organic waste adheres to the surface of these microbubbles and is removed as it accumulates at the reactor surface. This method first came from Germany and is termed the Berlin Method. In addition, a refugium which houses many species of macroalgae, including Caulerpa racemosa or chaetomorphae macroalgae is sometimes used to remove from the water excess nutrients such as nitrate, phosphate, and iron.Template:Fact Beneficial microflora and fauna (zooplankton) as well as small invertebrates (copepods and amphipods) are provided a space free of predation to grow and, when returned to the display tank, serve as food for corals and fish. Conventional combined mechanical/biological filtration used in fish only systems is avoided because these filters trap detritus and produce nitrate which may stunt the growth or even kill many delicate corals. Chemical filtration in the form of activated carbon is used to avoid discoloration of the water, to remove dissolved matter (organic or otherwise) and to help stabilize the reef system.

Water movementEdit

Water movement is important in the reef aquarium with different types of coral requiring different flow rates. At present, many hobbyists advocate a water turnover rate of 10x: 10 x aquarium capacity in gallons = required flow in gallons per hour. This is a general rule with many exceptions. For instance, Mushroom Coral requires little flow and is commonly found in crevices near the base of the reef. Species such as Acropora and Montipora thrive under much more turbulent conditions in the range of 30 to 40 times more flow, which imitates breaking waves in shallow water near the tip of the reef. The directions which water pumps are pointed within an aquarium will have a large effect on flow speeds.

"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."[3]
Reef ready tanks obtain at least a portion of the required water motion from the pump that returns water from the sump. This flow usually is augmented by other strategies. A popular strategy is placement within the display tank of multiple powerheads. Powerheads are simply small submersible water pumps that produce a laminar or narrow, unidirectional water stream. The pumps may be alternately switched on and off using a wave timer and aimed at one another or at the aquarium glass to create turbulent flow in the tank. Drawbacks to the use of these powerheads include their capacity to clutter the display tank, propensity for excess heat production, and the laminar quality of water flow often produced. Another method 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. Newer submersible propeller pumps are gaining popularity and are able to generate large volumes of turbulent water flow without the intensely directed laminar force 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.[4]

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 gases 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.


Main article: Aquarium lighting

With the advent of newer and better technologies, increasing intensities and a growing spectrum, there are many options to consider.

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.

Heating & coolingEdit

Reef tanks are usually 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), one may 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 place of a chiller. Fans cool the tank via evaporative cooling and require more frequent top-off of the aquarium water.

Water ChemistryEdit

Stony corals, which are defined by their calcerous calcium carbonate skeletons (CaCO3), are the focus of many advanced reef keepers. These corals require additional attention to water chemistry, especially maintenance of stable and optimal calcium, carbonate, and pH levels. These parameters may be tracked and adjusted with test kits and frequent manual dosing of calcium and pH buffer additives requiring no additional equipment. Alternatively, automated methods employing small dedicated computers with electronic water quality monitoring capabilites are often used to control water chemistry parameters via several components including calcium reactors and kalkwasser reactors. Calcium reactors are canisters filled with crushed coral skeletons. Carbon dioxide is injected into the canister acidifying the water and dissolving the coral skeletons. The acidified and CaCO3 rich solution is then pumped into the sump. The excess CO2 then diffuses out of the water and into the air leaving behind the CaCO3. Kalkwasser is an aqueous solution of calcium hydoxide, Ca(OH)2. The kalk reactor stirs the solution, preventing precipitation, and dispenses the solution into the sump where the Ca(OH)2 combines with dissolved CO2 to produce CaCO3. These components must be controlled by a computer to prevent dangerous changes in pH due to the acidic calcium reactor effluent or alkaline kalkwasser effluent.


Large volumes of highly conductive salt water, complex plumbing, and numerous electrical appliances housed in close proximity certainly pose a significant risk of damage to both person and property and require close attention to safety. All equipment should be used according to manufacturer instructions. Electrical equipment should be placed above water level whenever possible, and drip loops should always be used. Circuit limits should never be exceeded and all appliances should be plugged into ground current fault interrupter (GCFI) outlets. GCFI's are the type of outlets required in bathrooms. These can be purchased at any hardware store and are relatively easy to install. Plug in GCFI power strips are also readily available. Home monitoring equipment with water sensors can also be adapted for the home aquarist and used to alert the owner of power outages or water overflows. This equipment can allow for timely intervention in a potential disaster and provides an added sense of security for frequent travelers.

Nano reefsEdit

A nano reef is a type of marine aquarium that is typically less than 30 gallons. The exact limit that distinguishes a nano reef from a regular reef is somewhat ill-defined (some claim that anything less than 40 gallons would qualify), but 30 gallons seems to be the generally accepted limit.[5] Nano reefs have become quite popular in recent years among fish keeping hobbyists, primarily because of their smaller size, maintainability, and the possibility of lower costs. The burgeoning interest in this niche of marine aquarium science has fostered several notable contributions ranging from specific consumer products such as specialized aquarium filters, compact high intensity lighting systems and smaller circulation pumps. Such equipment allows the aquarist to maintain an environment wherein many marine organisms are capable of thriving.

Nano reefs are very commonly sold as complete kits which contain the tank, stand, power compact T5, T8, PL lamps or Metal Halide lighting, protein skimmer, UV steriliser, 3 or more stage filtration, a heater and a water pump or powerhead. However, many nano reefkeepers decide to upgrade their aquariums with better quality equipment such as a more powerful protein skimmer or lighting.

Pico reefsEdit

Another term gaining popularity is pico reef, which is used to refer to the smallest of nano reef aquariums. These tiny tanks require even more diligence with regard to water changes and attention to water chemistry because the small water volume provides little room for error. Care must be exercised when stocking these tiny tanks because too many inhabitants can easily overload the tank's ability to process wastes effectively. For the smallest of pico reefs, even the presence of a single fish is discouraged. Pico reefs often consist of live rock, hardy corals, and small invertebrates such as hermit crabs and marine snails.

Challenges associated with small reef aquariumsEdit

Because of the small water volume, nano reef aquariums require extra attention to water quality compared to aquariums of larger water volumes. Many experienced reef aquarists recommend testing the water twice weekly, with water changes at least every week.[6] In particular, ammonia, nitrite, nitrate, pH, salinity, alkalinity, calcium and phosphate levels should be monitored closely. When it comes to nano reefs, even minute changes in water conditions such as mild temperature fluctuations can be problematic, whereas the greater water volume of larger aquariums provides a more stable and flexible environment.

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.

Filtration in nano reefsEdit

Many nano reef aquarists prefer their nano reefs to be as natural-looking as possible, and therefore choose to use as few mechanical filtration methods as possible. The primary filtration method of choice in nano reefs is a good amount live rock and live sand, which are pieces of rock that have broken from the coral reef and are populated with millions of beneficial bacteria and organisms which aid in the dissolving of organic wastes produced by larger organisms in the nano reef. However, many other 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.

External linksEdit


  1. Fatherree, James. "Liverock: Answering Some Liverock FAQs.",
  2. Toonen, Robert, Ph.D. and Wee, Christopher. "An Experimental Comparison of Sandbed and Plenum-Based Systems. Part 1: Controlled lab dosing experiments." Advanced Aquarist 4.2 (2005)
  3. Adams, Jake. "Water Flow is More Important for Corals Than Light, Part V." Advanced Aquarist V.6.1 (2007).
  4. Adams, Jake. "Water Flow is More Important for Corals Than Light, Part V." Advanced Aquarist V.6.1 (2007).
  5. "Setting Up a Nano Reef Tank" by Jeff Yeramian, September 19, 2006, retrieved January 14, 2007
  6. - Water Changes.

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