I've read that deep scratches, particularly on the bottom and long sides of the tanks, are "weak spots" and more liable to bursting because the glass is a little thinner in scratches. That's glass aquariums atleast, I dunno about acrylic. I have a pretty deep scratch in the front of my new 45 gallon which I just noticed yesterday, and I wish I had put that side facing the back, but there was an ugly sticker mark on the other side which I didn't feel like removing so i put that side in the back. On that note, does anyone know if goof off, goo gone, etc is safe to use on the exterior of aquariums?