You've given me more things to think about.
My goal here is not to have crystal clear water, but something fairly clean that won't smell and won't be just a poop container.
In my current design, the filtered water flows back to the -bottom- of the pond. I was thinking maybe that would be enough to stir the muck-push it up to the top?
The splashing I was planning to overcome by covering the sides of the pond with wood so any splashing drip back into the pond
The poop settles, the food settles, the muck settles, the splashing mine do probably extends about a 3 ft. radius. I'm sure there are ways to overcome this, but I haven't figured it all out yet myself. If your substrate around the pond is something like gravel or wood or indoor/outdoor carpet, they won't drag as much mud in. If you have gravel in the bottom of the pond it will hold a lot of the muck and keep the water clearer and you could manually siphon the gravel on a schedule like you would the bottom of a fish tank. hmm...
I was reading this lately, and looking at biofilters in general...
https://www.tyrantfarms.com/how-to-build-a-backyard-pond-with-diy-biofilter/