A sump is an excellent choice of filter, particularly for a marine reef system. Sumps are best placed below the aquarium, usually in the cabinet (check dimensions). The main advantage of having a sump plumbed in to the aquarium system is the significant increase in water volume, making it more stable and less prone to fluctuations in salinity, pH and other water parameters. You can use the sump to house a huge amount of aquarium equipment such as protein skimmers, calcium reactors, heaters, etc. This will make the aquarium look less cluttered and help in achieving a more natural aquascape.