Yup that seems to be correct I did a few water changes and scrubbed the glass and it's gone.Looks like bio film. I get it sometimes on the front glass. I think its a combination of proteins and bacteria but maybe someone else can chime in.
Now I have a next problem, there is a bunch of tiny white worms in the tank, floating in the water column, it looks like dust in the tank but they are wriggling.
What medication do I need for this?