How to remove algae stains from glass

[Supergeorge123]

Recently i found an old aquarium laying on a sidewalk and took it in. The problem is that it is covered in algae stains that seem impossible to remove. Does anyone have suggestions on how to clean it up?

 

[A201]

A razor blade & cleaning strength vinegar might get the job done.

 

[SwampFins]

As long as its algae it should come off with a razor blade. Vinegar does help with some hardwater stains, but if you have an etched haze on the glass, that's pretty hard to clean up.