If I use gravity feed from the overflow, will I need an airstone or something similar?
For the operation of a DB ReefTech Protein Skimmer each unit requires one pump for its operation, no matter which configuation or model that is selected. The pump is what drives the protein skimmer, producing the small bubbles that make them work. For example, with the External configuation there are two methods of delivering water. One is by having the unit located within the sump and utilising the valve at the base to let in water. The pump attcched to the protein skimmer sucks the water directly into it. The other method is to have water fed to the protein skimmer; either by an additional dedicated pump (only purpose is to feed water to the protein skimmer), a bleed line off another system pump (for example the return, chiller or refugium pump) or gravity feed from the overflow (depending on the flowrate it may be required to direct some of the flow to the sump, rather than all to the protein skimmer). However, the protein skimmer pump is still required for operation.
