What is a refugium?

A refugium is a small aquarium that either sits under or hangs onto an existing saltwater or reef aquarium. A growing number of aquarists are replacing their sump filters with a refugium. A refugium typically contains live rock, macroalgae, and a deep live sand bed and is the best representation of how nutrients are handled in nature. It recreates, on a small scale, the seagrass beds that are commonly found in association with a natural reef.

How does a refugium work?

With a refugium, instead of the detritus and uneaten food becoming trapped in a mechanical filter where it decays, this material will settle within the rock and deep sand in the refugium, where the micro crustaceans such as amphipods and copepods will feed upon it. As a result, and since there are no fish in the refugium, the micro crustaceans multiply, thereby adding a natural food source and biodiversity to the aquarium.

A macroalgae, usually of the Caulerpa genus, is then grown above the rock and sand, and feeds upon the nutrients within the water. This not only aids in keeping these levels from becoming problematic, but will also reduce the number of water changes that are required. When the refugium is illuminated opposite of the main aquarium, it provides essential oxygen during the nighttime hours when the main aquarium is not illuminated, thereby reducing the nighttime pH fluctuations.

benefits of refugiums

Refugiums provide many benefits to saltwater or reef aquariums. They:

• Provide existing aquarium inhabitants with natural food sources such as phytoplankton and zooplankton
• Filter water naturally (dramatically lowering nitrate and phosphate levels) and decrease the frequency of water changes that are needed
• Stabilize water conditions (especially oxygen level and pH)
• Help control algae growth in the existing aquarium
• Add trace elements back into existing aquarium water
• Protect small organisms so that they can be self-replenishing. This works especially when you want to grow "feeder" organisms to a certain size so that they can reproduce before the entire population is eaten. Popular "feeder" organisms include feeder fish, amphipods, and copepods. For example: in a reef tank, a large enough refugium can provide a safe haven for copepods (where they do not have to worry about being eaten and can breed).