You really don't need a filter for saltwater. Most filter media picks up waay to much and will quickly become a source for nitrates. I'd look into buying some fine play sand from Mendards to give yourself 4-6" and investing in some live rock, a pound or two per gallon. These will definantly do the job for filtration. If things are built up enough, water changes become very minimal, and I know of several people that don't even do them, just top off the tank. Live rock is expensive, but if you buy half good stuff and half base rock, which is usually about a buck a pound, in 6 months they're both essentially the same thing. Oh, but you will need some good powerheads, but they're usually only $25 or so.
