When I checked my experiment late this afternoon, I found that the lettuce, spinach, and green beans had sprouted.
The water is 62F degrees, top to bottom. The food I've been putting in has been disappearing. Much of it could just be sinking to the bottom, but I know that at least some of it is being eaten by the larger bluegills that I've seen at the top eating it.
The timer I added cost about $16. The pump draws less than 2 amperes at 12 VDC. The pump is on for 56 minutes every 24 hours (8 times per day for 7 minutes each time). That puts me at about 2 ampere-hours per day of consumption. When spring comes, I think I'll make the whole thing solar just to prove to myself that it can be done completely without external energy sources.
Here in my little timer mounted in a weather-resistant housing:
And, here is the little greenhouse with the cover installed:
