Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Koi get REALLY BIG.
They will ultimately need 1000 gallons or more.
They are very hungry for plants, and they grow fast.
Ditto the other comments: Any plants will be short lived.
Set up a planted sump for nitrogen removal. Emersed, floating plants. Leaves in the air, roots in the water will be the best N removal plants. Water Hyacinth, Water Lettuce and other large, fast plants are best. High light. (sunlight).