Hi James Koi!
Good to hear from you, I've been wondering whats happening with the koi.
Last month I picked up a couple $12 32 gal. trash cans and set them by the tank. Using a cheep Harbor freight 400 gph pump, I transfer the 'fresh water' into the tank after water sets for 48 hours, chlorine/clorimine (?) is removed and temp has come up to match koi tank water without heating. No chemicals needed and I'm not adding any hard water from the hot water heater.
I wonder if you could do something with 4-55 gal barrels and change out the water more often?
My little Q-tank seems to be doing OK, I swapped out the up flow mechanical trash can filter for a 55 drum with a bottom drain, works alot better. Water is filtered before going into bio filter.
The koi have been really growing and want to be feed all the time.
I was concerned about overcrowding, but after talking to friend that shows koi, he told me more or less, as long as the waters fresh I should be ok, and that one long time koi guy used to keep 10-30" show koi in a 1000 gal tank over the winter.
For lights, 2-40w fluorescents (sun spectrum) on a timer 9am-10pm.
Mark