Yeah,
I have a Koi pond and a goldfish pond in the garden.
The Koi pond is 18' x 12' x 5' deep.
I use a Nexus 300 filter and UV to keep it clean, coupled with an aeriated bottom drain.
Got about 12 fish in there at the moment.
The Goldfish pond is full of mating frogs at the moment, have to keep fishing them out of the Koi pond or they drown.
Ken