| I don't see why you can't keep all three, Koi, plants and Goldfish.
Several ponds I've seen here in the UK have vegetable filters, i.e, a planted chamber which the filtered water runs through before returning to the pond.
A pond I visited in CA in 1990 had goldfish in one of the filter bays, albeit a large one.
So how about a vegetable fitler/goldfish pond as part of the system?
I would suggest that you have someway of isolating/bypassing it as some Koi treatments may be detrimental to Goldfish and/or plants.
good luck
Bern
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South East Section BKKS
and www.koipin.com |