Sump
Used extensively in marine aquaria, sumps are containers of water held outside the aquarium, which may be used to house filtration equipment, heaters, or other accessories. A sump tank enables the aquarist to house all the essential aquarium equipment away from the main aquarium for easier access and to allow greater rock-work or other aquascaping to be placed in the main aquarium. In most cases a sump tank works by water overflowing the main aquarium through a weir into the sump and then pumped back into the main tank.
