I thought a lot about the fish/plant balance and also about the heat inputs and finally decided to forgo the fish and use a biodigester for nutrients instead. I put a food grinder in the greenhouse and ground up all my kitchen scraps and threw them into the biodigester. Aside from the nutrients (which made the plants grow huge) it also made gas (stored in a stack of air mattresses), which I used to help heat the water in the winter. I also ran a heat exchange loop through a smallish compost pile made from my fall barn clean-out. The gas and compost didn't quite get the water up to the ideal temp for the anaerobes but things did keep going through the winter. I used 2 ibc tanks as digesters to give the anaerobes time to digest everything and tests for salmonella etc showed the water coming out clean before it entered the mixing tank, which circulated water to the plants. I filled the mixing tank with a bunch of biochar to give the nitro/nitrate microbes something to grow on. The growbeds were 2 20' x 2' tanks, one with grow media (gravel) and a deep water tank. The lowest point of the system was a sump tank with 2 small pumps. One on a timer (about 10 mins every hour) to fill the media bed and the other (continuous) to pump water up the mixing tank. The media bed was up on legs so it auto-siphoned into the deep water bed, which then drained into the sump. The mixing tank had an outlet at the top so, as the pump filed it up, it overflowed into the deep water bed. Serendipity-wise, the water glugged big air bubbles as it drained so I drilled a bunch of little holes in the outlet tube and it let out a steady stream of bubbles to aerate the water in the deep water bed. That bed also got a lot of aeration from the auto-siphon from the media bed and, as mentioned earlier, the plants all seemed extremely happy with very large white roots.
I was never comfortable with all the IBC plastic and foam insulation. But the plants were pretty amazing and I had tons of greens through the winter. All the engineering set-up was pretty interesting to me so fun was another output. I did like that my winter kitchen scraps had such a visible output via the gas. I could really tell what made the anaerobes happy by the amount of gas they put out the next morning!
This set-up was near Portland Oregon and is actually still there but I had to move to Wisconsin so it is no longer in operation (though my son keeps thinking he will get it going again someday). I never took any pictures but have a schematic on this website:
https://pacificart.wixsite.com/oday/community-classroom
