Sump=tank to hold water. You could honestly throw some waterinto a rubermade container and have a sump. Most people use a 20 gallon long, because you can do so much with it. Check out my refuge in my profile. Its not updated, but I will update it soon. If your going to have a fish only.....I would reccomend a wet dry. Its easy to take care of. you could always use a refugium though and it would do the same thing and it takes care of itself. And cool as hell to look at.If you use a sump, I highly reccomend a filter sock. It pulls out so much gunk its insane.