While simplifying my backyard PyraPOD, Richard and I have found we could fit four larger iAVS sandponics towers with one fish tank and three levels of sand grow beds in each corner. It is a 4-ponds in a larger pond setup. It can easily be changed to 4-ponds outside of a cross-shaped soap reservoir setup, which is better. While the large pond wrapping around four fish tanks can be built with half a meter digging and then laying pond liner in the ground, it is better to build the larger pond with concrete.
A story about Richard Nelson and his simple and yet unprecedented inventions