fuges can serve several functions, they can be used to reduce nitrates(DSB, macro), stabilize parameters such as PH and alk, and /or to provide a natural food source for your tank. what you are trying to accomplish will dictate the design of your fuge. most folks on here who use s fuge seem to use it primarilly to reduce nitrates, so DSB and macro are the order of the day, but liverock rubble is prime for growing pods for fresh fishy treats 24/7.