What’s this purple residue on aquarium glass?

[JakesAquariums]

This is a used aquarium that was sitting in someone’s garage. Been trying to clean it with hot water and vinegar, but this purple haze keeps appearing as it dries. Kinda reminds of how polarized lenses are. It is definitely a residue of some sort because the glass feels different (less smooth) in areas that are purple. Any ideas on what it is/ how to get rid of it?

[lefty o]

purply rainbowish speaks of an oily substance, id try dawn dishwashing liquid.

[Comradovich]

Would agree with @lefty o. Looks an awful lot like some kind of petroleum product residue. (And that would fit with being in a garage for awhile). Does it have a smell? If Dawn doesn't remove it, it may have permeated the glass. To get it out, I'd look in an auto parts store for something that removes grease stains. Not sure which products would be aquarium safe, but you're definitely looking at some kind of grease remover. I'd look at cleaning the stain first, then removing the stain remover with your vinegar and water later on. Smelling as you go, since chemical smells are a pretty good indicator of how well you're accomplishing the job.

[JakesAquariums]

Dawn helped some. Razor blade was the key. Looks like some weird fiberglass coating. Thanks for the suggestions. 👍

[nabokovfan87]

weird.  What brand is this lid?

could be some sort of saltwater crazing residue on the glass?