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 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. 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 but in reality can prove to be a very complex task. Some corals, such as mushroom corals and polyp corals, require very little light to thrive. Conversely, large-polyp stony corals such as brain coral, bubble coral, elegance coral, cup coral, torch coral, and trumpet coral require moderate amounts of light, and small polyp stony corals such as Acropora, Montipora, Porites, and Pocillopora require high intensity lighting. Of the various types, most popular aquarium lighting comes from metal halide lamps, 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