Originally Posted by Sakura8
That oily stuff is a protein film. It happens a lot in unfiltered tanks without water movement because of the high protein content in the food we feed our bettas. One member gave me a good tip for getting rid of it: place a paper towel on top of the water and let it soak up water. It removes the film.
The film is harmless but annoying.
The film is ALMOST harmless but annoying.
Since betta breath in atmospheric air, if they can't break through the film they can actually inhale some of it and then have to rinse it out of their labyrinth gland. Kinda like breathing through your nose while washing baby shampoo out of your hair in the shower, even tho it's fairly neutral it is still irritating.
I keep some worn out acrylic tank cleaning pads around, when the film gets on the water I dip one below the film then mop it up from below, pushing it and lifting the scrub pad out of the water slowly. This gets dust, excess food, oil, slime, bacteria and hair out really well too.