I did not use one on my 38 gallon. I only used 2 powerheads, with prefilters on them, and a Pengiun 200. It did fine and flourished without a skimmer for a year. But when I upgraded to a 72g bowfront, I knew I needed a skimmer. I have seen umpteen successful tanks under 40-50 gallons without skimmers, anything over that I believe it is more of a necessity.