...Oh, and back about a month ago when I was having all the trouble with tank lights and an undiscovered voltage leak, I had this thick, mutant surface crude that even the surface skimmer of my Prizm could not break up. I took a wisk and had to wisk the surface of the tank for about 2 minutes just so all the crude would flow into the skimmer....
If you do this, make sure you've properly scared the fish first so they wont come to the surface.