I feed mine all the time. They tend to grow very quickly if they're fed. I feed mine mysis, krill and fortified brine (same stuff my fish eat). They are greedy little SOBs.
They like moderate light and moderate flow, and have the same general requirements as other LPS. They aren't considered difficult. I don't know why yours would be dying. I started out with three little acan frags/colonies, but my large female clown decided she was going to hate on one particular one. She kept kicking it off the rock into the sand, no matter where I'd put it in the tank. Even if I glued it down. Last time I left the state for work, I asked NDB to keep an eye on it, because Clowny was going after it with a vengeance. I came home and found it face down in the sand, flipped it over, and it was covered in brown jelly. I asked NDB, "Didn't you see it? Why didn't you pick it up off the sand?" He was like, "Ohhhh... Sorry..."