Overflow filter systems are typically used in salt water aquariums, but can also be used in freshwater aquariums. One of the main reasons overflow walls are used is to avoid flooding in the event the wet/dry filter and/or pump system fails (e.g., because of loss of power to the pump, etc.). Overflow filter systems have an overflow wall or barrier that extends continuously upward from the floor of an aquarium tank surrounding a filter intake region. Water in the main region of the aquarium tank flows over the top of the overflow wall into the filter intake region. Plumbing for a remote wet/dry filter system and a return pump is usually installed through the floor of the aquarium in the filter intake region. In a conventional system, water in the filter intake region flows by gravity downward out of the aquarium tank through a drain to a remote wet/dry filter.
Often a standpipe is included as part of the drain to raise the water level in the filter intake region of the aquarium. A foam pre-filter is sometimes mounted on the standpipe. After being filtered by the wet/dry filter, water is returned to the aquarium by a return pump. Although the return tube is typically installed through the floor of the aquarium in the filter intake region, the outlet spout for the return tube returns the filtered water to the main region of the aquarium tank outside of the filter intake region.
In a typical overflow filter system, water thus circulates throughout the aquarium system as follows: 1) water from the main region of the aquarium tank flows over the overflow wall into the filter intake region; 2) water in the filter intake region flows through the pre-filter and falls by gravity through the drain to the remote wet/dry filter; and 3) filtered water from the wet/dry filter is pumped through a return line to the main region of the aquarium tank outside of the filter intake region.
In conventional overflow filter systems, splashing noises are created as water spills over the top of the overflow wall from the main aquarium region into the filter intake region. Gurgling sounds are also created as water flows through plumbing associated with wet/dry filter systems. The gurgling sounds are generated because a significant amount of air becomes entrained with water flowing through the aquarium drain, and the entrained air can often produce gurgling sounds. Some people find the splashing and gurgling sounds to be annoying.