I am getting ready to set up a 90g that a friend gave me. The tank has a box filter on the back that is driven by a pump, which also runs the skimmer. I think he always called this a systems tank but dont remember. My question is since the tank is not drilled should I keep the box and pump or go with a external overflow w/sump? What r the pros and cons?? Any advice would be greatly helpful!!!! Thanks P.S. the box is not a normal filter like your normal aquaclear just for clarifacation.