54"x24"x24" is approximately 130 gallons capacity. An Eheim 1262 is rated at 900 GPH open discharge and right at 800 GPH at 4 feet of head. I have always preferred to keep my return pump in the 5x the display volume capacity so 5x130= 650 GPH which should be right in line at 4.5 feet of head. I have always found Eheim to be a little conservative in the GPH and head capabilities so it may be slightly more if plumbed for minimal headloss. Always install a ball or gate valve on the discharge side of the return pump so you can throttle back or fine tune the flow a little if needed so the overflow, standpipe and sump function efficiently and quietly.