As long as they are setup properly they work fine for their rated tank sizes..but then again it all depends on whats in that tank to begin with...........Srt skimmer power head within 2" of water surface not deep as depicted in the directions, and keep outflow tube at or slightly above water level of tank...........works like a champ. MIne has been skimming merily along and doing just fine for awhile now and required no fiddling, and is ppulling some nice dark green/black skim, and virtually no micro bubbles being infused into the tank, and working without the bug ugly bubble diffuser box too....Its Q U I E T! Coralife SUper Skimmers IMHO have the best bang for the buck and do a very good job.