Why won't this energy generating motion machine work?

My vision is two vertical tubes, one has a dense liquid and one has air. A ball falls due to gravity and generates energy from the force of gravity. Then it only takes a small force to get it to the tube with the dense liquid (denser than the ball) and then it will rise and just need a nudge to fall again. I have not figured out how to get the ball into the tube at the bottom and have the liquid sealed but I'm sure there is a way.