Filtration for today's reef aquarium is more about water movement than actual filtration. Many of the new aquariums come predrilled with overflows already installed. This configuration requires a sump mounted under the aquarium in the stand to catch the overflow water and pump it back to the tank. The sump typically has bio balls that the water trickles over for biological activity. The sump usually has room and chambers for mechanical filtration, carbon chambers, heaters, chillers, and protein skimmers. The pump can be external or inside the sump. Many sump filters have been replaced by refugiums. The typical reef aquarium has a water movement of about 10 times the gallons of the tank. For example a 100 gallon tank should have a water flow of 1,000 gallons per hour, but not all of this needs to go through the sump. Through the use of power heads you will be able to quietly and efficiently create a great deal of water movement. As a general rule, it is better to produce this current from multiple outlets rather than one strong return, reducing dead spots with little water flow.