What's the best way to clean acrylic tanks?

[bluegiraffes]

I just got an acrylic tank to replace my old tank but it's so fragile I can easily scratch it with my pinky nail. My old one was covered in scratches because I didn't know how to properly take care of it and I want to try to preserve my new tank as well as possible. What's the best way to clean off the calcium deposites and algae without scratching the tank? If it does get scratched, how do I remove them without buying a kit?