A large O. scyllarus can't break an acrylic tank and it won't scratch it, but it can dent it. We have lots of acrylic tanks and occasionally animals will try to dig through a corner or strike at one another. This can leave tiny dings that after time can cloud the surface. I can't imagine that this would be a problem with a home aquarium, but in my lab, it is a problem I have come to live with.
Roy