Are you having any particular issue with your tank? Typically, a tank that small would be fine with just water changes and no skimmer.
Look into the hydor slim skim and the slim skim nano. decent quality skimmers for the smaller tanks. You dont want a huge thing taking up alot of space in your tank. Unless you have a sump......then you have more options
180g Reef - 60g Rimless Reef -90G FOWLR- 125g Malawi Cichlids- 40b REEF- 34g Fresh Planted-working on- 20L FOWLR- working on
I have a mix of many different saltwater fish amongst my tanks, but I love my Tangs most of all.