Good one! I can't imagine burning a hole into my frag tank, then the resulting crack, and subsequent flooding.
Not at all. Acrylic, especially in tanks, is quite translucent. A laser won't have any visible/negligible effect... however on a molecular level it's likely to weaken the structure resulting in a small breach in acrylic over time. It's vital that the laser be aimed at the appropriate entrance angle in order to maintain your tanks structural integrity...
I'm joking. It'll do nothing to your tank