inside glass coating with a hard film.

[jeanej1]

This is hard to describe but it's like the calcium that builds up above the water level but this is below the water level and makes the aquarium glass blurry and foggy looking and in order to get it off I need to scrub with a very abrasive scrubby till my arm falls off. I have been trying to clean little sections at a time because I don't want to stress out my fish having my arm scrubbing like crazy just to remove a tiny section. My water levels all read fine and I recently started small water changes with my python while cleaning the gravel. My fish seem to be a little lethargic lately. Any suggestions why this build up is on the inside of my aquarium?
Thanks :
Jeanie

[Amidicus]

These guys need specifics on the water quality in order to be helpful.Ammonia,nitrite,nitrate,ect. levels.What are small water changes?You should be doing 20-25%(of the tank) water changes weekly.Water quality is vital to healthy fish.