it's dependent on the footprint of the tank. a 125 is usually 6' long x 19" wide x 24" tall, a 180 is usually 6' long x 2' wide x 2' tall and a 240 is usually an 8' long x 2' wide x 2' tall tank. so if you have the space my recommondation would be the 240. if you don't have space for the 8' tank just make sure you go with something that is 2' wide at a minimum, IMO.