Does it have an overflow? If it does, i'd do a sump with a protein skimmer. I have had really good luck with mine. It also lets you get the heater and all that junk out of your tank and out of sight and your tank will never look not-full. If not and you can't drill one, try a HOB skimmer. Stay away from HOB filters and canaster filters. They are great for Freshwater but not so great for salt. You will also need some power heads. In all honesty all you really need is live rock and water changes but if you have them money, get a good filter system. It will make your life better trust me.