Is a Refugium NECESSARY?
Refugiums are a form of natural filtration that has become quite popular in saltwater and reef aquariums because they are an effective and low-maintenance solution for ongoing nutrient export. They also help support biodiversity in the aquarium, support a natural food chain, and boost your aquarium's biological filtration. While refugiums are not mandatory or necessary, they can help you maintain a much healthier enclosed ecosystem and/or replace the need for more labor-intensive maintenance and costly media.
Benefits of a Refugium
A true refugium consists of a sand or mineral-rich mud substrate, some live rock, and live macroalgae. The substrate and rocks provide habitat for both beneficial bacteria and micro-fauna (copepods) while the macroalgae consume nitrate and phosphate as it grows. The refugium shares water with your main display but should be isolated in such a way that fish and other tank inhabitants cannot access it. It will also require a full-spectrum light to provide the necessary light energy for the photosynthetic macroalgae. The macroalgae are harvested on a periodic basis carrying the sequestered nutrients out of the aquarium.
While nutrient export is the primary function of a refugium, the habitat it provides for bacteria, pods, and other organisms increase biodiversity and supplies the display aquarium with a steady supply of this beneficial micro-fauna. These tiny creatures not only help clean up the aquarium by consuming decaying organic matter but also provide food for hungry fish and invertebrates.
In some cases, hobbyists may choose to forego the sand substrate and live rock and only grow macroalgae in a bare chamber for the sole purpose of nutrient export. This approach is a bit easier and still effective for the removal of nitrate and phosphate but does not provide the same biodiversity and biological filtration benefits. Some purists might even argue this minimalistic approach should not be labeled as a refugium but rather algae filtration; similar to a chaeto-reactor.
In either case, refugiums are simple by design and very easy to set up and maintain, even for first-time tank owners. The benefits have been proven and the more growth you can achieve out of the macroalgae, the more nutrients you can remove. The larger the space you have for that macroalgae, the more it can grow which essentially means scaling the impact of a refugium is quite simple. The bigger the 'fuge, the more capacity it has for nutrient export.