Backyard Aquaponics
A place to discuss aquaponics

Ducks clear out most pests from the garden and have cast iron stomachs.

There is one main problem Jensilaedi with your idea of no external inputs. You have an output so the loop is not closed. When you eat food from your garden that nutrient is lost. The only way to have no input is if you have no output. Im not going to get into the humanure debate here cause its been done too many times already, and its gross.
I buy the big bags of food from BYAP shop and it works out very cheap in the long run. Storage is a problem but a good feed bin will keep the food for ages.

Duckpond, no argument there, it's just, it'd be nice if I could - should there ever be a need to, to just live at home on the food without having to go out and get something to keep the system going...
If I ever have my own farm, I'd have a goat, a few rabbits, a few pigs, lots of bantams and ducks as well as a couple of horses..
each has their own purpose in the ecosystem and AP is also part of it.
hmm I guess there has to be some sort of input to enrich the system otherwise if using the same resources over and over might make it go stale. solar and water is kinda an input as they come from the sky I guess.

If I didn't understand your point here, then I wouldn't have understood AP!! AP has a lot of that going on. water enter tank, then water leave tank!