ok here goes. I just dug a 4000 gallon pond that i haven't decided on a filter for yet but here is what i'm thinking.
pump from the bottom drain with a 2500gph up to ground level and the same from the surface skimmer i'm installing, controlling the flow of each by using ball valves.
first stage will be a pool skimmer trap for large debris from the surface skimmer. then a 55gallon drum with a cleanout drain and charcoal, and filter matting for finer particles.
the pumps will be placed at this point. from here i will use a areator in the system before sending the water through a 6 inch 10 foot piece of sewer pipe filled with bioballs, and then to the waterfall.
by using ball valves and unions the system will be easy to build but would it work for a pond or will it work at all?
it will run with the ground and be covered with a faux rock bench for viewing with access to the cleanout points.