ireven & EUPHORIA,
I love my shark. They are really considered not reef safe because they don't care what they run into when they swim and are also kinda clumsy when they swim in aquariums but so far he's hasn't hurt anything. I feed him krill shrimp once a day, most feed every other day, which I'll start doing when he's a little older. During feeding time it's always a contest between him and my flounder of who gets the next piece of shrimp off of the feeder stick. Sharks will definitely eat all the shrimp you have in the tank, but my peppermint has still managed to avoid him. It's a bamboo shark so he'll eventually reach about 2.5 to 3 ft in length but that will take years and hopefully I'll have an even bigger tank by then.
patricia,
I would not put an achilles tang in a 55, he'll most likely die very quickly that is much too small of a tank for that fish. I had a foxface rabbitfish in my 55 but they do get huge over time so if your gonna upgrade just buy fish small so you have plenty of time to do so. The same thing with the blue hippo tang, all tangs are swimmers that's all they do swim and graze, I know a lot of people with them in 55s but they are not supposed to be in a tank that small. I would probably get a cool wrasse instead they swim as much but don't need as much room, are much more hardy, and there are some really cool looking ones out there (check out the pic of the filamented flasher wrasse, not a great picture but awesome fish). The urchin and duster cluster are no problem.