Sticking mucho light over a small tank like that is always going to give you temperature problems, else you could just use sunlight. If you want something a bit different some of the LPS that require manual feeding would be possible, combined with many water changes to get you round the water quality problems that feeding will cause.
I would be shy of trying to replicate some very adventurous, advanced aquarists like melev if you really aren't sure of what you're trying to do. Alternatively try to find the thread in reefcentral.com on Anthony Calfos nano. 2*36 watt pc's + 100% weekly water changes works very, very well ona 5 gallon.