Abstract: An aquarium overflow filter system having a pre-overflow wall with openings therein improves circulation of water throughout the aquarium tank. The overflow filter system includes an overflow wall that separates the tank into a main aquarium region and a filter intake region. An intake for a wet/dry filter is located within the filter intake region. A pre-overflow wall located outside of the filter intake region encases at least part of the overflow wall to create a mixing chamber therebetween. Openings in the pre-overflow wall allow water to flow through the pre-overflow wall into the mixing chamber. The openings in the pre-overflow wall can be strategically placed to attain a desired circulation pattern within the aquarium. Water pressure at lower openings in the pre-overflow wall tends to move water upward through the mixing chamber, thus water from all the openings eventually flows over the top of the overflow wall into the filter intake region.