Re·fu·gi·um:{–noun} a zone designed to allow pods to breed without predation; an area to grow macroalgae.

A refugium is a container or a portion of the sump used to grow macroalgae, which helps prevent nuisance algae from taking hold in the display tank. As the macroalgae grows, the hobbyist culls, or harvests, some of the plants (as much as 50%) every few weeks. This not only encourages new growth from the remaining macroalgae, it also exports nitrate and other unwanted nutrients naturally from the system, starving nuisance algae in the main reef. Another benefit is that the algae provides a nice area for pods to live and breed, safe from all predators. The refugium is not a place for fish, shrimp or crabs as they would consume those pods. Remember, it is a refuge or predatory-free zone!

Some sandy substrate is nice, which can be merely 1" or as much as a deep sand bed if the vessel is deep enough. Some live rock rubble and some macroalgae like Cheatomorpha are all that is necessary to create a very interesting and useful biotope to your reef system. A few snails can keep the surfaces clean in that zone, and a cucumber can keep the sand clean of detritus.

Some systems have huge dedicated refugiums tied into a multi-tank system. Others are quite small, even using a modified hang on back filter as a tiny refugium as you'll see in these slides. If space is limited, I recommend trying to create a section that is a minimum of 10% of the display tank's volume. My 280-gallon reef has a 29-gallon refugium, my 55-gallon reef had a 5-gallon refugium and my 29-gallon reef had a 10-gallon refugium. All three tanks benefited from that zone, and none suffered from common nuisance algae. Copepods, mysis and mysids would breed, and their babies would flow into the display tank as a food source for mandarins and other fish.

In the sumps I've built, I made the refugium's water level 12" high. The baffle is 13" tall, with teeth cut 1" deep. If you would like to skip the teeth, you can glue or wedge a section of eggcrate along the top of the baffle to keep the macro algae and snails where they belong.

A refugium needs some type of light over it for the macroalgae to grow. My preference is a 5100K spiral compact fluorescent bulb, which I run on a reverse photoperiod, from 10 p.m. to 8 a.m. daily. (When I used to keep Caulerpa nummularia, I found that leaving the light on 24 hours a day prevented it from going sexual. It was an easy solution to an annoying problem. In California, Caulerpa sp. has become so invasive that is it illegal to own it. More information at www.sccat.net )

Adding a refugium is fun. You will spend many hours studying the fascinating activity going on in there. While my reef was asleep, I spent many late nights on my belly watching the pods scurry about as worms wove their way through the plants. Who knew so many little guys would be so interesting? Use your ingenuity to create a pretty planted tank. Add a few mangroves if you like.

This basic overview should help set the stage for those of you considering adding a refugium to your system, and this thread will answer a number of questions you may have. Enjoy the slide show, and be sure to note both the variety and imagination these hobbyists certainly have. Talk about 'going green!'