They need huge tanks to survive. They are very easily stressed and very quick. They usually end up racing around the tank and banging into the walls killing themselves......hence the need for a bigger tank. I love em.
They are fragile, require pristine water conditions, and a HUGE tank. I wouldn't consider keeping a lookdown in less then a 200 gallon, and then I'd be nervous. Great eaters, fast swimmers, just need a LOT of room.
