Berlin Sump System
The word "sump" usually refers to the section that contains the pump or pump intake. However, in the case of a Berlin system, which is a completely open tank, the entire reservoir is sometimes referred to as the "sump."All of these systems have several things in common. Because these filters are open systems, they can only be fed by water drawn from the surface of the aquarium. If they were fed from below the surface, the filter below would overflow and flood when the pump was turned off. Therfore, they all require the use of an overflow prefilter of some sort, either built-into the tank or of a design that hangs on the back of the aquarium.
Which Do I Use?
The big question we always are asked is, which to use? In general, if the aquarium has live rock in the aquarium or in the sump, then a Wet-Dry Filter is not nescessary, as a matter of fact it is just a holding area for detritus (garbage from the tank), and not really desired. The biological surface area on the live rock is awesome for the good bacteria to form and adhere to, and provides the best possible biological system growth. Tanks with live rock for biological media usually are unscathed by large fish loads, since the biological system is so strong.
If the aquarium being built is a fish only system live rock is not desired, then a wet-dry filtration or sump system is very nescessary to grow the needed biolobical media for a stable aquarium environment.
How about a refugium?
A refugium is a sump where a partitioned area has been added to grow marine plants that absorb the nitrates in the water. These nitrates act as fertalizer for the plants, and keep the nitrate level in your aquarium at 0 or very close to it. A refugium can be a second sump system added to the aquarium, or it can be the main sump system, with a partitioned area dedicated for the main pump, a dedicated lit area for the marine algae, and a dedicated area for a protein skimmer.