Mystery white stain outside glass

[Coleman612]

I got this tank for free so surprising holds water. Everything is fine except the front of the glass has this weird smudgy white haze that won't go away. I've tried different kinds of cleaners and nothing works. Even seems to make it worse.This is not in the water but the outside of the glass. Any clue as to what it is and how I can fix it?

[JaredShope1]

It almost looks like a chemical spill. What you could try is some windex and if that doesn’t work, try some type of razor blade scraper to see if you can scrape it off. It may even just be the glass is old and it is died from something and it’ll never come out. If this is the case, you could just flip the tank the other way so no one will see it

[Sniperhank]

Try to clean it with some white vinegar and see what happens.

[kbalaz]

it almost looks like it is some sort of adhesive residue. Like a background was glued on it at one time. If not, hard water deposits that have etched the glass. If it is etched, its not going to come off no matter what you do. You could try Bar Keepers Friend and a sponge, if that doesn't take it off, it is etched in the glass.