A 'fuge' is a very unclearly defined addition to the system. Rock and macro, macro and sand, macro and mud, rock and sand, are not a clearly defined methodology. Without a clearly defined task in mind, a 'fuge' is a waste of time.
First, mud was a huge hoax. It accomplished nothing that was claimed it did. Rock in a sump has no purpose either: all it does is produce more nitrates. This leaves only two other options, and they are mutually exclusive. If you do one, don't do the other. Using a single tasked sand bed, is a good method for reducing nitrates, if done right; if done wrong, it will rapidly pollute your tank. Part of wrong is having anything else in the same "task zone" such as macro, rock etc. Macro is an 'ok' method for reducing nitrates, (the DSB works far better,) however, if combined with a sand bed, you have problems with the sand bed. As an added twist, it is far better to run a "DSB" remote from the sump. Combining two or more specific tasks, in one container (section) turns the method from export, to production and is self-defeating.
Clearly, the refugium has a defined task, but requires seperate export facilities in a sump type system common with the DT—a refugium is a high production zone, not an export zone; as it is implemented in sumps, it has no task at all...it has no clearly defined purpose, a common practice you "have to have"—but who said so?
