Refugiums, also known as "reef aquariums" are aquariums which are set up as a means to naturally sustain the fish and other organisms (such as mollusks, live algae, sponges and more) in the system. This is accomplished with consistent high-water quality, which is maintained by using a specific set up of high-end filtration and lighting.  

Maintaining this "live" aquarium culture is, in the minds of many who specialize in creating refugiums, a way in which to keep the life structure of the oceanic reef "alive" in the comfort of one's own home. The complex life system of our ocean's reefs, and all of the organisms within it, make for a home aquarium what is termed as "live sand" or "live rock"-essentially, sand and rock that is teeming with naturally sustainable life. Refugiums not only embrace and sustain marine life, but they usually encourage new life as well; reef species usually grow and reproduce at much higher rate within a refugium system than they do outside of one. 

The key to setting up refugiums is the caliber of equipment, especially lighting and filters. Full-spectrum lighting, originally designed for industrial use, is commonly used for an indoor reef system. In fact, lighting is one of the most important factors in establishing and sustaining natural reef life, as many reef life forms base their behaviors on natural light cycles.  

Likewise, a great filtration system is equally important, as consistent water quality is one of the most important aspects of maintaining a reef environment. The filtration system designed for refugiums has actually been modeled after those used in sewage treatment plants; the level of filtration is extremely complex and powerful, and typically comprehensively filters the environment as often as several times per hour.  

Most aquarium hobbyists only go so far as to monitor their tank's temperature, saline/ammonia/nitrate levels and pH. Those who work with refugiums also focus on the water's oxidation, ultraviolet radiation, and electrical current, as well as the levels of phosphates, calcium, silicon and more. Supplies and kits for testing aquarium levels are widely available in several brand names. 

It's good to keep in mind that the procedure for setting up an indoor reef system can be so complex that it's best to do some in-depth research to make sure what types of lighting and filtration will best suit your needs. There are several resources online and in books for researching the topic; just try not to get overwhelmed by the complexity and sheer amount of information. While setting up an indoor reef system can, ultimately, be as complex as you'd like to make it, it can also be tremendously fun. Just remember the general rule for setting up refugiums (maintaining the highest-quality water with the smallest amount of effort) and you'll have your indoor reef system up and running in no time.