Brown film on surface of water

[molybdenumman]

In the past week or two, my tank has developed a brown film on the top. I have a maxi jet 900 moving the 55 gallons of water in my tank but it doesn't seem to affect the brown scum. The powerhead is about 3-4 inches below the water level.

Has anyone encountered this brown film and possibly have some suggestions to get rid of it? Is my powerhead too low in the tank?

My water conditions appear to be good, nothing too out of the ordinary.

MoMAN