CBB,

You bring up some good points, many of which we've considered.

If you reduce the fish density, then you could turn off the pumps for a period of time depending on that density. Considering this, you could run the system during the day on solar, assuming the sun is shining, and turn off the water pumps at night.

Reducing the fish density will not necessarily reduce the nutrient value. As long as the fish to bio-filter ratio is maintained and the fish to plant ratio is also maintained the fish to water ratio can be reduced by increasing the amount of water in the system. This can be done by increasing the size of the fish tank. It will take longer initially to build up the nutrients but given the above, they will be maintained. This will also make the system more stable, meaning that it will take longer for it's chemistry to change.

You must, however, maintain a high level of dissolved oxygen in the fish tank. It would be best for the fish to have their final daily meal several hours before turning off the water pumps in order for the fish to produce their final waste of the day and for it to be processed.

We have looked at a sustainable system, including fish food, and to some extent you can capture the part of the vegetables you grow that are not consumed, desiccate it, grind it up and pelletize it. For the most part, you need to live in a climate where you can grow and store fish food by using standard soil planting techniques in order to have enough food for the fish year round. You can also desiccate the leftover fish parts and process it along with the veggies for fish food protein.

As an aside, we purchase palletized fish food in large quantities relative the amount of fish we have, bag it in one gallon zip locks and put it in the chest freezer until we are ready to use it. We do this because left unfrozen, it has a short shelf life.

Vegetables are mainly water. Once desiccated they are mainly carbon, which is sequestered from the CO2 in the air. The fish are the same. The fish food, then, does not make up most of the mass of the fish. The fish waste does not make up most of the mass of the vegetables. So, there is no perpetual motion going on here. It is possible then, to grow enough fish food in the aquaponics system to sustain the process.

Worms may be another alternative for fish food. Others here can chime in on that option.

Fish are sustainable as any fish farmer knows. Plants are sustainable as any tillage farmer knows (unless Monsanto gets involved).

As for sustainable power, I am an advocate of ethanol. You can grow plants that have a high gallons per acre (over 1000 gallons per year) of ethanol. Ethanol can be used for running a generator when the sun is not shinning. Ethanol can be stored for long periods. A century ago, almost every farm had an ethanol still for running farm equipment before Rockefeller backed the suffrage movement in order to stop its production and get petroleum as the only fuel for automobiles through the guise of probation. It is now legal in the US to have a still and the permit is easy to obtain. Ethanol is making a huge comeback in the US and around the world. I'm not talking about the politics of ethanol, but its use as a sustainable fuel. As for the politics of ethanol, there is a large effort on the part of the Petroleum Institute to get people to believe that in it some way makes food prices increase, which is pure propaganda on their part.

Aquaponics has its down side as you have indicated. It should be considered as a part of a greater whole when when looking at a total sustainable solution in case of WTSHTF. Or, as the flying nun once said, when the fertilizer hits the ventilator.

I believe this would be a good topic to pursue on its own on this forum.

Oliver