Going bigger. The wife and I are looking at a 700 plus Cube Aquarium. Thats one of my main points that I will agree is that most people do buy these sharks and don't realize that the do get bigger reguardless of the size of the tank. Thats the key thing. We have a Electronic store in CA called FRY's they have a 5ft Nurse in there display tank that is a Cylinder. I'm not saying that most people who look for sharks realize that the Nurse will get big. However there are a few that have the funds and can get tanks that could house a Nurse. I would say its to the LFS to inform before selling. I know in Cali. most LFS its special order. even the Whole sellers here say the same thing.
A 700 gallon will not last for very long either though. Not just upgrade to something that will last longer?