Are you running a DIY CO2 by any chance?
It looks really similar to something I observed a while back. - I had a bucket of water taken out of the tank during a water change, and I was going to use it to water plants over the next day or two. I dropped in a couple of beer bottles, and the next day there was a thick whitish film all over the water surface. my best guess was it had something do do with yeast introduced from the residual beer. (I've had several water changes sit around for a couple days without this happening, but I tried a repeat for verification, and sure enough, the next day the bucket was full of whitish surface scum.
As to removing it, you could always dip in a small container (like they use in delis, for take out soup, etc.), and just drain off the top. It's a bit tedious, but works pretty well for removing whatever is on the surface, including duckweed if you ever have a problem with that.