Add to it and make your reef happy!
Normally installed below the aquarium, sumps receive water from overflows where it's then processed by filtration and other equipment before going back into the aquarium with a return pump. Sumps help increase the entire volume of a system and allow the use of generally more efficient filtration and equipment and keep them from being eye-sores in the display.
We highly recommend using a drilled aquarium with an internal overflow system, but when that option's unavailable, a great alternative is an external overflow box. External or hang-on overflows offer an easy way to set-up or expand a system to use a sump. External overflows use suction and gravity to take water up and over the rim of the aquarium and down to the sump for filtration.
A sump and overflow can be nearly as important as the aquarium itself and that's why Ready Set Reef offers the best of both from top brands like Eshopps, Reef Octopus and more.