Normally mechanical filtration is not needed with a reef tank. There are times when it is easiest to remove phosphate with phosphate remover used in a mechanical filter, or there are tanks with such a heavy fish load that water clarity is a near constant problem, so carbon is used to make the water more pleasant to view through, or if there is a need for intense lighting and you also have fish in with your corals water clarity must be good, so carbon is occasionally used. A good portion of reefers just put a bag of medium in their sumps where water must flow through it instead of using mechanical filters. This is not an option for those with out a sump. If a person has not already bought a mechanical filter I recommend a fluidized bed filter such as those sold for using phosphate removers. They work exceptionally well, are fair priced and can be stored out of site easily when not needed. They require small pumps and use small enough flows that they will work very well with small tanks or large.