Used tank, Cloudy glass ?

[Citrinellus]

Try ph down.

 

[gomezladdams]

Glass can get etched over time and that wont come off.

 

[SpeshulEd]

Try pool acid. Just make sure to wash it off well after use.

 

[SemperFish]

soak it in vinegar/water and then hit it with the razor. if you dont feel a texture the glass might be etched and you cant take that off. if theres texture to it then its some kind of deposit you can scrape or grind off.

 

[Thomas V.]

I cleaned my 2'nd hand tank i bought with the stuff i also use to polish my car windows, worked pretty well

(Wash everything out very good before filling then lol)