Most people don't use a skimmer on that size nano.I guess because most of those tiny skimmers aren't very good.Maybe someone with a nano can recommend one.I think could do without one if you keep up with regular water changes.
I been looking for one on my 12 gallon aquapod, to no avail, sapphire makes one but its like $100... My tank only cost $150... So I just stay on top of the water changes and I think it does ok...