I bought a used tank, and am getting ready to clean it and sterilize it before setting it up. All around the tank close to the top is some kind of deposit on the glass. I know I've read on here what to use to clean this off, but now I can't find it.

Can someone please tell me what to use on this?

It is most likely a hard water mineral deposit. This can usually be cleaned with plain white vinegar. Soak a towel in vinegar and let it sit on the deposits for as long as you can stand - hours will be good. Then rub it off.