Instead of commercial fertilizer, chicken droppings fall through wire mesh strung across the pool’s deep end, nourishing the algae & duckweed in the pond below. The tilapia eat the pond plants, release their own nitrogen-rich excrement, & the fish water then gets funneled (using a solar-powered electric pump) into the hydroponics system that grows the family produce.
This family converted an unused swimming pool into a greenhouse that grows produce tilapia fish, and chickens for eggs. Pretty ingenious. (There must be some mistake though, why would rainwater go with gray water?)