1. It is a simulation for teaching purpose and it is assume there is no viscoity(ideal fluid).
2. No matter what you did. The magnet need to move from air (lower pressure region) to bottom of fluid (higher pressure region). Otherwise, it is not a continue workable loop.
You need to do WORK to move magnet from air back into fluid again.
The WORK you need at least should equal the energy you gain when it move up.

From my point of view: It is not a workable device and it violate the physics principle I have learned. 
So I would not be able to create a simulation for you. Sorry!