Carl:
Good to see you back on the board...re: your enclosed pond...
4' x 7' x 4' deep would give you 810 gallons...enough to get you started... I have 6, 24+" koi in our 900 gallon pond...
Visited a new club member's house this week and he has a small 3x7x1 at the entrance to his front door...water is pumped up to the 8' level and allowed to cascade down the lava rock wall, maybe you could do something similar to increase your off gasing and increase you O2... His filtration is inadequate at this time and he plans to enlarge the pond by going down and changing to a Bead Filter, after he completes his current project of enlarging his backyard pond...
Like you, he's an architect but took it one step further and started a very successful construction company...Can you imagine having a Construction Company with all the equipment, manpower and money to build any pond you want... Something for you to think about when you get home... Jimmy started from scratch...
Food for thought, to go along with the sushi, shashimi and beru...
Aloha! Mike