byron:
You are going to need something more along the lines of 8,000 gallon.. at the very minimum you could use a 5,000 gallon... but thats the minimum.
Nurse sharks will eat every tank mate. So don't even think of having other fish in the tank with it. They should all be considered shark food as of right this moment. They will eat fish 5 times the size of their mouths and 2 times the size of their bodies. They eat massive amounts of food and will cost you easily $15-$30 a month to feed, if you feed them the food they need.
Nurse sharks will grow 7-9 inches per year and gain 4 to 5 pounds per year. If your tank is not big enough and they get large enough they have been known to and will thrash and possibly break the sides of your aquarium open. Then you will have big problems. It is also important for you to find out if you have a female or male, because the males will eat more, but the females are far more destructive and will get larger quicker.
So I suggest you start saving up because your nurse shark will grow massive amounts in a short period of time. And believe me, it is almost impossible to get rid of a large nurse shark.
Jim