Mechanical filters are inexpensive and almost always installed inside the pond. A pump is located inside a filter box and draws water in through layers of filter mats. Some mechanical filters have the pump attached to a filter with tubing. The pump pulls water through the filter mats and releases it back to the pond.
Water can be released back into the pond through a waterfall, spitter, fountain head or nozzle, of one of several homemade devices.
Mechanical filters should only be used for small pools of water. A whiskey barrel, homemade flower pot pond, a small preformed pond, or other pond under 500 gallons. Any pond over 500 gallons should be equipped with both mechanical and biological filtration.