About a month ago I noticed a very fine layer starting to build on the surface of the water in my 72 gal aquarium. I really didn't pay a whole lot of attention to it until it started to get a bit out of control covering the entire surface of the aquarium. This is largely due to the undisturbed water on the surface (I keep the filter return a few inches below the surface.
It really needed to be taken care of so I hunted around on the net. One guy used his python drainage system, inverted it upside down in the tank and skimmed the top layer out of the aquarium during his water change. Another suggestion is to get a skimmer attachment.
I'll likely have to revisit this again, but for now I just used the paper towel method. Clear out the top, make sure the light isnt going to fall in and zap you. Then lay out a paper towel flat on the surface and absorb up the layer of scum (bacteria, protein, oil, whater the heck it is). Took me about 10 towels to clear the surface of any noticable scum leftovers (the picture above is just general pond scum, not my aquarium :-)
Photo by otfrom