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Reef aquarium

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A reef aquarium or reef tank is an aquarium containing live corals and other animals associated with coral reefs. It is considered to be one of the most difficult aquarium setups to create and maintain. In recent years, advancements in our knowledge of the reef, coupled with more refined reef maintenance techniques, the reef tank has become much more accessible to the hobbyist.

From theme reefs 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 coral from around the world. Unlike the marine aquarium which main purpose is to house various fish, the true stars of the reef tank are the coral and other invertebrates.



The aquarium

The first step in building a successful reef aquarium is the tank itself. Most hobbyists prefer what are called "Reef Ready Aquariums" which are identical to regular glass or acrylic style tanks save for 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. Water pours over the overflow into and down the standpipe, through PVC piping, into a sump, which houses various filtration and heating equipment, through a return water pump and finally back via more piping through the second hole into the aquarium. An alternative method to having a tank that is already drilled is to use a hang on tank overflow with a U-tube (via a continuous siphon).


Unlike the marine aquarium that use a combination of mechanical, chemical and biological filtration, reef aquariums primary filtration 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 which is supplemented by powerful protein skimmers. This method first came from Germany and is aptly termed the Berlin Method.

The typical rule of thumb is to use from .75 to 2 pounds of live rock per gallon of aquarium water depending on the density of the rock or filling the tank up 2/3 of the way to the top. The benefit of using live rock is four fold: First, live rock acts as a biological filter, adding beneficial bacteria. Secondly, it introduces an abundance of marine life to the aquarium that many fish, invertebrates and corals use for food. Thirdly, it provides a natural reef appearance with ample places to locate corals. Live rock also will help balance and stabilize PH in the aquarium.

Mechanical filtration is often avoided because sponge filters, filter floss and filter socks trap detritus and produces nitrates which stunt the growth or even kill many delicate corals. Chemical filtration is used sparingly so to avoid discoloration of the water, to remove dissolved matter (organic or otherwise) and to help stabilize the reef system.

[edit] Water movement

Corals are simple creatures with limited ability to feed, reproduce and rid themselves of waste(metabolites).

An example of a closed loop water cirulation system
An example of a closed loop water cirulation system

Water movement is key to the success of the reef tank with each type of coral requiring different flow rates. At present, many hobbyists advocate the 10x rule: 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 while many species of Acropora thrive under much more turbulent conditions in the range of 30 to 40 times more flow most likely due to their proximity to wave crests in the wild.

Of the many different types of creating this needed water flow the most popular method is by using multiple power heads which are simply small submersible water pumps. The pumps are randomly switched on and off using a wave timer. Each aimed at the flow of another power head or at the aquarium glass to create a random flow in the tank. Another method gaining popularity is the closed loop by which water is siphoned from the main tank to a pump that in turn pushes the water right back into the aquarium via multiple returns to create water turbulence.

Water flow is important to bring food to corals. No coral relies 100% on photosynthetic food. Gas exchange occurs as water flows over a coral, bringing oxygen and removing gasses. Without water flow corals die. Water flow helps reduce the risk of thermal shock. Temperature of a corals surface can be significantly higher due to infrared radiation in slower water flow. Faster water flow aids in preventing thermal shock, reducing the temperature of the corals surface.


Another hotly debated topic is aquarium lighting. With the advent of newer and better technologies, increasing intensities and a growing spectrum, the topic of aquarium lighting can be a daunting one even for the seasoned aquarist.

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, Acropora Coral, Brain coral, Bubble Coral, Elegance Coral, Cup Coral, Torch Coral, Trumpet Coral can require substantially more intensity.

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: Light Emitting 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 there are several advantages that these systems bring 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 use simulate moonlight and the phases of the moon.

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 & cooling

Most hobbyists agree that a reef tank should be kept at a temperature between 78 degrees and 83 degrees Fahrenheit (26 to 28 C). 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. Chillers, on the other hand can run well over $400 USD and are more difficult to locate. For many aquarists, installing surface fans and running home air conditioning suffice in the place of a chiller.

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