Need info about saltwater shark and tank build

[Treebeard]

OK, an on topic post. In my opinion, you will need a very, very large tank to keep these sharks in captivity, at least the size of an Olympic swimming pool. I base my opinion on my observations of seeing these creatures swimming in their natural surroundings when I am scuba diving. I am making no comment on other fish available in the fish trade. If the original OP wants to say, "while, what about this fish.." we can debate that elsewhere.