The only filter you need is the protein skimmer. The liverock will do the rest of filtering provided you have a good amount of water movement in the tank. I would look for a skimmer rated for atleast 200g. Euroreef, ASM, Octopus, and MSX are all good brands. They will cost about 300-400 new so I would for a used one on ebay or craigs list. If you do use anything for mechanical filtration: filter sock, floss or sponges, they have to be cleaned at least once or twice week. So that they start to produce nitrates. Avoid bio balls like the plague. If you have liverock in your sump make sure is completely submerged all the time.