what is this on the surface of my tank?

[naesco]

Take a kitchen plate and dipping it slightly allow the skimate to flow into the plate until all the slick is gone. You may have to do this a few times

[jtbadco]

sounds to me like a combination of needing more skimming and more surface flow.

I would turn up your skimmer (if possible) or get a larger one and aim your powerheads towards the surface of the water