[Reefmack]

Laurent - on that surface film I'd advise keeping the tank level just a bit below the black rim, so that you can see a little air space at the top of the gate - that will allow the film to be able to be be pulled into the back compartment.

Then move the gate up a bit at a time till it starts skimming the surface. If you move the gate up too much the water level in the back compartment will drop too much and the pumps will start pulling in air & making more microbubbles in the tank.

I'd also keep one of the powerheads pointing up enough that you get some ripples on the surface - that will also help break up that film, plus get more oxygen transfer into the water.