i just got a used fish tank and the person had a diy backround and the silcone came off but theres a smudge on the fish tank i used a razor blade the smudge wont come off and i also used vinager also can someone help me
At home depot they sell an air freshener called simple orange, it is in with the cleaning products. It isn't designed to be used as a cleaner but it takes of stuff better than any cleaning product I've ever used. We use it at work to remove tar, etc. etc. It is only a couple of bucks for the can and you will find all sorts of uses for it.
Rub the smudge with a dry cotton cloth or dry paper towel. It will gradually burnish off as you present new cloth to the smudge.
Very few chemicals affect cured silicone including the normal soaps, detergents, and solvents.
Those that do dissolve it are too dangerous to be used around the aquarium. So mechanically wearing the smudge away is the safest method, even though it is tedious.