Oops, sorry if I wandered into something bigger here.
Rupert, first of all I know the design/implementation would be first rate as you have done this plenty of times. You have too many projects completed for anyone to consider otherwise.
What I was trying to point out is that maybe aquaponics isn't the panacea to all that "ails the world" and any implementation is going to require significant amount of ongoing work (that we are ALL guilty of never calculating the true costs of).
Basically yes our aquaponics system may deliver vegetables and fish on an ongoing basis cheaply but there is a cost associated with this that WE MUST CALCULATE and that popping around to the shops to pick up some cucumbers/capsicum DOES NOT HAVE THIS COST.
I see the same thing when people calculate how much backyard chickens cost, they work out eggs per week (in summer at height of laying season) and use this to divide the feed purchase with a per egg cost and then wipe away the difference between this and store bought saying.....oh well its way better for you...
The only way we as backyard farmers (and some of us as commercial farmers) can advance the field of aquaponics is by looking at ALL of the inputs required such as labor/those little $20-$40 here and there parts/feed and of course our TIME at a reasonable $ per hour figure.
Then we can truly calculate how much that head of lettuce cost us.