John Hakim's 5.5g Reef Tank. John explains, "this is the Left-End View of my 5.5g reef tank which has been setup for slightly more than 6 months now. Unlike other nano-reef tanks, I use a sump for filtration which has mechanical, biological & chemical filtration. It also has a small co-current protein skimmer."
Smaller tanks make great Do It Yourself (DIY) Projects. They are fun, easy, inexpensive and go together quickly. Just modify the DIY 55g Glass Aquarium Plans to meet your needs. There are a number of Canister and Power Filters and Mini/Nano Reef Tank Lights which will allow you to keep corals in your new tank.