I use a vortex. My pond is only 200 gallons. Vortex filter, stream, and
settlement add another 500 or so gallons. I plan to remove plastic pond and
replace with liner, this spring. My current setup gravity flows from pond to
vortex. Three pumps are fed from vortex. (Two pumps running, in warm weather,
and one back up)
www.aquaArt.com has good diagrams and also supplies vortex filters and bottom
drains, if you are out west.

Bill

Central Virginia