you dont really notice it. Its only when you are taking pictures. So you have to go at angle to were you a stright on at the coral rather the at a right angle to the glass. I have a 155 bowfront and I dont notice it.
I have a 46 gallon bow and i never really notice any thing bad. I also have a good friend with a 150 bow and there is not any noticable distortion. Good luck with the tank