500+ I'd say.
And you gotta consider the tank size too.
Overall maintaining a shark aquarium is abit overkill.And 6ft is too small for a Black Tip.Wanna stay in a toilet stall for the rest of your life?They can grow up to 6ft.
And the shark will be the least expensive of all the equipment you will need,like a tank[Needs to be round],Food,water changes,health and so on.
Would strongly advise you to consider your decision..
Or you can go ahead and watch the poor shark die slowly.
Sorry for harshness but it's true.