you can buy a sump with a refugium built into it. they do this using baffles. you could plumb one in seperatly from the sump and display tank, or the easiest way is to get a small hang on unit and just hang it off the tank. these dont have a lot of room in them, but they are effective non the less. i would start with a sump and a refugium right away or if you do the hang on design, you can wait untill your ready for coral, and then set it up. i would go to google and type in the general search, refugiums and read some articles on them. some will use a pic to show some items you can have in it.