sacred sump
A sump is a kind of reservoir, the lowest point in a system of circulating liquid, like water. In an auto engine, the oil pan is really the sump. It holds the extra oil that is not actually circulating through the motor.
In an aquarium, it is usually a container of some kind, like a smaller tank, located under the main fishtank. It has a pump attached, either submerged in the sump, or connected to it by a hose. The pump sends the water from the sump into the aquarium. The water returns to the sump either through an overflow box, or an opening in the aquarium just below the water line. These systems are common in marine aquariums, where the returning water passes through filtration media. Because the media is exposed to the air, it is much more effective than submerged media, oxygen levels remain higher, etc. The overall water volume is also increased by the sump's gallon capacity.
Any blockages can be disastrous in these systems. A failure in the return means the sump's contents, usually many gallons of water, will be pumped into the aquarium, and overflow from the aquarium itself, all over the floor. These problems can be avoided, but it can be tricky. Various water level sensor switches can be employed, and there are some nifty cut off devises that are virtually foolproof. I have two sump systems running, on two very large sw aquaria, and have not had any problems in many years.
I credit the local New Jersey fishgods for watching over my aquaria, and preventing any problems from developing.
