Best way to control surface scum?

[WeepingCrown]

So I have a 6.5 gallon planted tank with a Betta, 15 shrimp, and an infestation of assorted snails from a bad batch of Giant Duckweed that I had failed to clean off before introducing into my system. For the longest time I have noticed that I get an accumulation of unsightly surface oils that are difficult to get rid of. I have tried a surface skimmer but it just keeps sucking in my duckweed. I have researched ways but to no avail. I guess I'm just out of luck and my only option is to remove the duckweed and plop a surface skimmer in there once in a while. I just wanted to check with you guys if there are other ways to get around it.

 

[Delapool]

I found water movement from the filter and less light seems to reduce it. Sometimes I’ll resort to using paper towel if haven’t had time for a water change.

 

[fishwonder]

Put some plastic mesh screen around the surface skimmer.