I broke down a reef tank about a year ago and just wanted to go with a different look for this tank, no real reason for not having live rock. As far as the overflows are concerned, the tank is AGA and you are right they rate the boxes at 600 gph but I think that is way under rated. I have a Friend with an AGA 110 with a single box and he runs a Mag 18 with no problem for about a year now, also the pump is circulation only and is losing very little flow due to head pressure (perhaps -200/300 gph). Is your 180 AGA, oceanic, custom? Any pics?