I would put some plants in now.....hold offon the goldfish, forget about
koi....put in a lily (shade from the lilypads) hyacinth (roots filter the
water) and let it cycle for a week or so.....it will get green after the brown
settles....so when you add a couple fish you might not see them for awhile till
it clears again.

Stay away from chemicals, use nature, it is an easier balance.

Good luck enjoy each addition.
Maureen