You won't get rid of the surface grunge completely unless you have an overflow. Skimmer such as Prizm, Bak Pak, Remora have add on overflow box that you buy for extra. They generally do not work very well unless you keep up w/ your water topoff.

To get rid of surface grunge temporarily, use a white, chemical & dye free paper towel to soak out the surface grunge.

Edit: I meant paper, now power