Oily Film

[Pan]

I have a 20 Gallons tank that has developed an oily film on the surface, since this has started the water smells as well...not bad..just smells. I don't have the room for a hang on overflow for a sump and the big protein skimmers are too much for this little tank (size and cost). I am getting a new tank in a bit here then i will get the 20 drilled as well. I was looking at the fluval surface skimmer as a solution, i do water changes weekly, 15-20 % but the film comes back. is there a good qay to get rid of it...or is it something you have to live with when running a 20 gallon?