An oily film, by itself, is fairly normal on a reef tank, caused by dissolved organics interacting with the surface tension. That's why overflows use surface skimming. But if it smells petroleum based rather than fish based, that could be a problem. Dip a bowl or cup into it, sinking only a tiny bit below the surface to skim it out, and once the surface is clear, try a different pump. If the film returns, it's probably just what I mentioned. BTW, are the corals better today or worse?
Someone stop me! Please! But... not just yet...
55 Gal Tropical FW
55 Gal Mixed Reef