Sump filters can contain large amounts of filter media such as bio balls, cermaic media, alphagrog, living rock, foam or floss - plus plenty of other types of media, as well as water heaters, auto water top-up devices, calcium reactors and other equipment. A sump filter can be designed in many configurations, the most common being the up and over trickle filter design. The sump filter is sited beneath the aquarium in a cabinet. Water is gravity fed from the aquarium via an overflow weir into the sump. The filtered water is then returned to the aquarium using a return pump and pipe work. We recommend using the Herbie Method for connecting an Overflow Weir to the sump - quiet operation, easy to maintain and easy to install.