I get the oily film. More from some bettas than others. My 2- split 5 gal has tons and has a filter. While my split 2.5 w/ no filter has almost none with Allie and Storin in there, but when Ula and Carp were in there, it was thick! So i have no idea! Guess it's like some people sweat more, some bettas oil more?? 
