I should have taken the advice of everyone during my last build and gone bigger, but I didn't. Our Koi grew so quick in the little pond we had to build them a larger one. The end result is 16'x 8'x 4'. I rented a bobcat and dug it out myself. We used a bottom drain coupled to 4" plumbing into a 150 gallon stock tank. We went with more of a formal wall for the waterfalls. We wanted to do a higher pool feeding into the main pond, but our backyard landscape doesn't really go with that. The waterfalls are driven by an evolution 2500gph external pump. Its whisper quite. We have each fall plumbed through a gate valve for required maintenance and flow control. We also have an outlet with a hose hooked up to water the plants and garden directly from the pond.