The duckweed growth is not sustainable in a goldfish tank because the goldfish eat it faster than it can reproduce, and the guppy population growth is also not sustainable in a snapping turtle tank because the snappers consume them faster than they can reproduce. However in an isolated tank of just guppies and duckweed, the guppies are too small to consume the duckweed and there is no predator slowing the population growth of the guppies. Makes for a perfect live food culturing tank. #guppy #duc