Brown film

So i manually skimmed the surface of my tank before the water change and i appear to have caught what was there, looking from the bottom of the tank upwards, it almost appeared to look like a oil slick covering the tank surface.
its gone now, i am hoping to never see the SNOT monster ! LoL

Thank you all

 

I have the same thing right now but my anemone blasted poop all over yesterday so I guess that's what it could be. I was thinking I needed to cut the lighting period down.

 

This is exactly what I think it is, my Cody did a similar thing over the weekend, I think I am going to stop feedling shirmp and crab