it removes dissolved organic waste from the water. unfortunately with skimmers, you get what you pay for. you can get they $30 cheapies from your local ***** and these are CRAPCRAPCRAP! lol. personally i would reccomend the aqua-c remora, which runs about $125. excellent HOB skimmer. however, if you arent planning on adding anything other than these three fish, and keep up with regular water changes etc, you should be able to omit the skimmer.