Hello reefers!! I want to upgrade my return pump to a Neptune cor-15 I looked up the dimensions of my sump and it does not look it will fit I heard that pump can be mounted externally too. My Return Pump Section: 4.5"L x 6.5"W and the pump is 3.875" W x 4.875" H x 6.250" L This is the data I collected from BRS I attached a picture of my sump hoping that will help.