“This is a planter and a fish tank. You put your regularly potted plant in this pot on top, and a goldfish on the bottom. What could they provide for each other, you might ask? Waste! Yes, the fishes turn their eaten bait remnants into nutrients for the plant, while the water fed to the plant is filtered as it passes though and becomes clean for the fish. It is a totally natural and lovely system.” - Source

This is a planter and a fish tank. You put your regularly potted plant in this pot on top, and a goldfish on the bottom. What could they provide for each other, you might ask? Waste! Yes, the fishes turn their eaten bait remnants into nutrients for the plant, while the water fed to the plant is filtered as it passes though and becomes clean for the fish. It is a totally natural and lovely system.” - Source