Just curiouse why your wanting the hang on the back kind? there good, just usually smaller. Look up a filter called " Skilter " There pretty good and not to expensive. there a hang on type, with built in skimmer. Ive heard good things about these Skilters. you can find them on ---- , i dont think SWF caries them. I order all my fish , and pretty much everything else from Salt Water Fish .com except my filtersystem. let me know Todd