The filter system
With a little experience with the biological filter (in the aquarium) something like that was also conceived, but much larger. Maybe not ideal, but as long as it works, its fine for me.
The filter system is below the little bridge between the two ponds. In the back is the koi pond, without waterplants.
In the front the plant pond is situated, with a couple of goldwinds. The water of the koi is filtered and brought back to the koi pond using the principle of communicating vessels.