dont take my recommendations without looking at others. I am getting a custom refugium made. I am fairly new to saltwater tanks so I dont want to give false information. I am basically relaying what I heard from others back to you.
With a refugium, instead of the detritus and uneaten food gets stuck in a mechanical filter where it decays. Where as in a fuge, all this material settles within the rock and the sand, where copepods and aphipods will feed on the material. As a result, and since there are no fish in the refugium, the micro crustaceans multiply, which gives you a natural food source and biodiversity of the aquarium.
What are the benefits of refugiums? (I googled this..)
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
Serve as temporary acclimation tanks for new inhabitants
May possibly aid the immune systems of fish (it is speculated that many species of macroalgae release compounds into the water that boost immunity in fish)
After development, provide considerable aesthetic value to the system