Koi ponds use bottom drains that feed into swirling chambers that sling the poop out and it settles to the bottom of the chamber and you periodically flush it out. That's the big tall brown thing. Usually you bury those next to the pond and have it gravity feed into the separator so the poop doesnt go through the pump first. Space limitations kept me from doing it optimally though, so the vortex chamber is post pump.
The vortex chamber empties into a 4" pipe that gravity drains back to the pond coming out the sidewall of the pond about 12" under the water line.
The skimmers feed into the bio-chamber/sand filter and it collects lots of gunk too. The bio chamber is back washed once a week to get whatever the skimmers pick up flushed out. The bio-chamber loop feeds back to the UV light, water fall and pond side jets. There is a system of valves to balance the flow out between the 3.
Maintenance consist of back washing the bio-filter and flushing the vortex separator once a week. Thats it. There is a drip system from my well water that keeps it topped off and it has an overflow built into the gravity return line of the vortex to maintain pond level.
I have 16 koi in there now. All small. All water testing comes back 0ppm 0ppm 0ppm so far.
It needs a stronger pump on the skimmers and I think I want to put a traditional pool sand filter before the bio-filter to keep the crud out of the bio-media a little better and help take water clarity to the next level.
Right now it is running 3 low head pond pumps from W.lim. (2x) 1/3hp and (1x) 1/2hp pump on the center bottom drain.
All the pumps, UV and filtration system came from W.lim out of California.
www.wlimproducts.com
How is the cement made water proof for your builds? Coating or what?
The pond was built like a pool. It is plastered and tiled like a traditional pool install.