White film on waters surface?

I was wondering if anyone can help me?  I have a 30 gal planted tank 
with an UGF system using two powerheads. I have a cloudy white film that 
looks oily floating on top of the water.  I remove it one night via 
scooping and paper towel and the next day it's back again ??? Any help 
would be appreciated.

Adrian Hydon <aph at globalserve_net>