The Refugium

The popularity of marine plants in the aquarium is no more evident today than in the introduction of the refugium. The use of a refugium is a natural, beneficial way to balance and promote a healthier marine aquarium. A refugium can be defined as any separate system that is connected to another tank for the purpose of creating a protected environment for beneficial marine flora and fauna to grow without predation by fish and invertebrates. They typically contain small amounts of live rock, various macro algae, and a deep sand or mud bed. These systems can not only improve the water quality of marine aquariums by removing nitrates, phosphates, carbon dioxide and some metals, but in time can provide a live food source for many marine species by hosting different larvae and invertebrates. A typical system is illustrated to the right.

They're many commercially manufactured refugiums available today in a wide array of styles and sizes to suit almost any desire or need. Many of these add-on systems are getting larger and more advanced so that hobbyists with large aquariums can enjoy the benefits of a refugium with reduced maintenance and care. The most popular style of refugium is one that is placed directly under the main tank as part of a continuously flowing system that allows the tank water to move through the sump and then back into the main system via a return pump. This style often includes a pre-filter sock or other media that traps large debris before entering a separate lighted chamber where marine macro algae and/or plants are grown. Most models also have separate chambers for a return pump and/or a protein skimmer. For those wanting a larger surface area or a more custom design, a simple system can be made out of almost any container or aquarium sturdy enough to hold sand, rock, water, etc. Dividers can be made of cut sheets of glass, acrylic or screens to separate the mechanical and biological components.

For aquariums that lack the space below the main display, there are several options. First, a separate tank can be placed beside, behind or above the main display tank and plumbed with an overflow box and/or bulkheads. This style can present some challenges, but allows for the most visibility and enjoyment of the refugium. Another option is a small hang-on-the-back refugium as illustrated to the right. These smaller versions can be added to systems that lack the appropriate space under the aquarium. These most often include a small circulation pump that draws aquarium water from one end of an acrylic box and out the other end. Although small in size, they can be effective in smaller aquariums up to 30 gallons. 

Flow rates can vary greatly in these systems, but most favor a high turnover ratio, as much as 10x the water volume per hour. Larger display tanks featuring corals and invertebrates can benefit from even higher flow rates. In their natural environment, most marine flora and fauna live in a dynamic place, with strong currents and constantly changing tidal surge, so they are quite accustomed to adapt to varied levels of water movement.

Light fixtures for refugiums are readily available and many are actually built into the design of the lid. Led lighting is by far the most popular choice but it should be full spectrum as actinic and blue light doesn't provide a useful wavelength for most algae species. Some have had success with both red and yellow light but this spectrum tends to fuel the growth of undesirable micro algae as well.

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