When i got my 55g, i hate how he had paint on the back. So I took a razor blade to it and there are no scratches from that job. I highly regret removing it though
I did a quick search and found this paint remover. http://www.ecosolveamericas.com/
They say it's solvent free, so it shouldn't harm the tank.
I'm sure you could find a similar product at your local hardware store.
Test a small spot on the bottom where you won't see it.
I did a 100 with blue paint on the sides and back. Sucked. Gotta get a lot of razorblades and just do it. Im not a chemical guy..pain in the ass, but like he said, get a ton of em and go at it. Its a pain but little bit of effort and good to go. Plus you wont breathe in that crap or risk anything on the tank. It was nearly impossible to scratch it if you take your time.