You should have either a skimmer or a refugium. It'll keep the tank freer of nitrate build up and if you plan on keeping coral, the proteins must be removed or broken down. Refugiums break down proteins whereas skimmers mechanically remove proteins. For small tanks like that, a Prism should do great. It has a slim design and hangs off the tank. The one for your size tanks goes for about $100. You could probably find it cheaper online.