Algae on Surface of Water

[Angry_Platy]

I have just noticed a thin film of green algae on the surface of the water in my 75gall tank....there is not a lot of algae in the rest of the tank as I have one adult bnose and 2 baby bnoses taking care of it....My 30gall tank doesn't have the algae and beside the surface of the water, it seems normally crystal clear.

Is there a reason for this? Why ahs it happened so suddenly? How can I get rid of it?

Hoping someone can help