"k" wrote
I am the token lazy ponder.
We filter by
- having lots of water
- few fish
- lots of underwater plants
- lots of rocks in the waterfall.

Same here,
I use an air pump for aeration, lots of plants but no water pump and no
filter. I only have golden shiner minnows which just build up to a
sustainable population and size.

No filter, no UV, no water pump, no Koi, no feeding, no problem.
--
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18,000 gallon (17'x 47'x 2-4') lily pond garden in Zone 6
Cheers, Steve Henning in Reading, PA USA