Design for fowlr n reef tank should be the same. For freshwater sump and marine sump, generally has different. For freshwater sump, think got more compartments to allow multiple media filtering. For marine, we have 3 main compartment, filter stage follows by equipment stage(skimmer, reactor, media, etc) and finally to return pump stage. More space catered for middle stage to allow flexibility in equipment addon etc. Hope this help.