The oil is normal, it's protein and bacteria and such. It's nothing harmful, and may actually be helpful to your tank.
I wouldn't worry about it - you can continue to take it off twice a day if you don't like the way it looks, otherwise, leave it alone.
It may have something to do with changing treatments and adding salt, but not necessarily. My tanks get it, and I don't bother removing it, it doesn't bother my fish at all.
I wouldn't worry about it - you can continue to take it off twice a day if you don't like the way it looks, otherwise, leave it alone.
It may have something to do with changing treatments and adding salt, but not necessarily. My tanks get it, and I don't bother removing it, it doesn't bother my fish at all.