the coral would usually be the one that didn't make it. It definately can work in a tank, but like I said, see what you are hoping to have, as far as livestock goes, in the end. If you figure out "the one thing" that you just have to have in the tank, you can build the rest of your livestock list (corals and fish) around your one goal. It's a much easier way than seeing a random coral or fish, and buying it only to find out that it isn't compatible with something you'd been waiting patiently for...