In setting up a reef aquarium, the best setup to use is what we call a Berlin setup. It consists of a particulate filter, some sort of chemical filtration (usually carbon), and a protein skimmer which removes dissolved organic waste from the water. Biological filtration in a reef tank is done by the live rock in the tank, so you will need to get enough of it to do the job. The equipment is usually located in a sump tank down in the aquarium stand, with an overflow box to deliver water to the sump and a strong pump to return it to the tank. Strong specialty lighting is also required for the corals; today the LED
lights are a good energy-efficient option. Be prepared to spend some $$ and don't let sticker shock slow you down; reefing is a rather expensive hobby ! As I said, read up all you can on the subject !