I get film on all my 5 tanks. Pressurized or not. I have soft water in at least 3 out of 5 tanks. Plants are in all my tanks. I do not use pellets to feed my fish. Regarding the Ehiem surface slimmer. It works well , but it takes a lot of CO2 with it when running. I have found out that leaving on a timer does not work well either since it rejects film back out of the filter as soon as its turned off. Why would my tank be different than yours? Fact is, if you watch the filter after it shuts off more film will drip back out.
My solution is: Running it when CO2 is on because its more convenient for me but only for an hour or so. I make sure while it is running , I lift it up out a liitle to keep the spill way above the water line to keep film in the filter then I pull the plug. It is a PITA, but a solution until the next day when the film returns.
The only other real solution would be to run a sump. You would never get the surface film when running a sump. Sorry folks, thats life without a sump.
I have checked many times, just like HOB filters, the skimmers suck the life out of your CO2 system. Yes, you could double up on your gas. But I will not be doing that. For now I babysit my skimmer since it keeps the water clear for about 12 hours until the film returns again. The paper towel method is pathetic. Frequent water changes helps but will never totally get rid of the film in the long run unless you did like 50% water changes 2 times a week.