Neptune COR-20 DC Return Pump. Up to 2000gph (COR-20)INTELLIGENT, QUIET, ENERGY EFFICIENT Your return pump is by far the most important piece of equipment on your aquarium. It circulates the water which is basically the life blood of a tank. Creating a great aquarium is just like building a great body it all starts at the core and this is precisely how our pump got its name! The COR is a variable speed, brushless, DC driven centrifugal water pump designed specifically for aquariums to be intelligent,