Cleaning an empty fish tank with heavy build up...?

[xxpaul17xx]

Hello all, I just got a 75 gallon fish tank. The tank is empty but the person who had it before me left water in it for about a month with no filtration or antyhing. There are spots of heavy build up where the glass looks foggy and is kind of sticky and a ring that goes around the tank where the top of the water level must of been wich is also a foggy look. I was wondering what would be an easy way to remove this to have a nice clean, clear tank again. also it is an AGA tank. Thank you!