Outdoor ponds in backyards are generally built to mimic streams with pools and differ from the real
thing in one very important way. Natural streams are open systems. The water is continuously replenished from upstream.

Backyard ponds are closed, recirculating systems and the water must move continuously through a filter to maintain clarity. If the pond houses fish, the filter must have both mechanical *and* biological capability to deal with particulate and chemical wastes (ammonia, nitrite) and must run continuously. As you build, make sure your pond is designed to avoid dead spots and select pumps, filters and aeration systems robust enough to keep running all season long. Your goal in filtration is to put the entire volume of your pond through the filter once an hour, and both the pump and the filter need to be able to sustain and accept that flow.

Our website has articles and a lot of information in the Q&A section that should help. Please go there before you finish your build. It might save you considerable trouble and heartache.