Thank you for your helpful comment, really appreciated.
We've already carried out a multiphase simulation to model the air bubbles, and we have also simulated the fish waste. It is essential to include the aerator in the simulation as it enables us to observe how the resulting air bubbles are distributed depending on where the aerator is located.
Do you have any ideas/hints on how to simulate it?
We also think of simulating the gates but the porous media thing seems to not achieve what we need