You should be fine.
My experience with contractors is they will be glad to take your money and tell you what you want to hear. They wave their hands around, feel the wall, put their ear to the floor, swing a dead chicken over their head and pronounce it safe to put an aquarium there. Not like 5 years down the road if something ever did happen you could find them. They would just lie and say you told them it was going to be a smaller tank or this or that. I hate contractors(no offense). If it's on a load bearing wall (outside wall) and the beams are running perpendicular to the tank it will be able to carry more than enough weight.
skeeter