I'm not much of a handy man and did not have any room for a sump or anything else below my 50gal reef so I did purchase the hang on unit from CPR. They are small and expensive but work very well. There is a powerhead which pulls water into the refugium and a syphon which carries it back to the tank. The only problem is they do not come with a light so you will need to attach one yourself. If you lack space under or around your tank, are not a DIY person, and are willing to part with $100+ for a small refugium they are worth it as mine has been up for 3 months now it's full of pods/algae and my trates are at 0 (even with biowheel filtration)