My dad found this stuff in his garage and gave it to me for my tank. You use it on the outside and it removes minor scratches as well as improves the clarity of the Acrylic. It made my tank look brand new again. All you do is wipe it on with a soft cloth, let it dry, and then wipe it off with another soft cloth. It's like car wax for acrylic tanks. Anyway, you should try it if you can find it, it would be in the auto section or in an auto parts store.
It's great stuff!