In most older reef aquariums water was drawn out of the tank either from the bottom or from approximately halfway up the tank. All advanced reef keepers agree that this is incorrect. The fact is that nitrogen gas, along with other elements, rises to the surface of the water. This can be observed by the existence of a “scum line” at the water level of the tank. It is at this surface waterline that you must draw the water to feed the skimmer. This ensures proper gas exchange between oxygen from the atmosphere and the nutrient-rich water that rises to the surface.
This concept of surface skimming will employ either overflow pipes or a dam-type wall over which surface water flows out of the tank. For filling the tank by using the main pump, my personal preference is to have a spraybar at the bottom rear of the tank. I believe this results in a truer water flow and exchange throughout the tank.
In order to have a true modern reef tank, surface skimming of the water is essential; all water flow out of the tank must be from the surface. This water then enters the protein skimmer, where the bulk waste products get removed. Then the water passes through the prefilter.
Simplified Reefkeeping
