Skimming Issue?

[SLAYCHILD]

On my 29 the top layer of water is not skimming!! I see like an oily layer on the top of the water. I have a skimmer and an over flow. Why is it not skimming the surface? Please help

[gjuarez]

I would add a powerhead to agitate the surface. Its odd that the overflow box is not skimming the surface, normally they do a great job at that.