When you feed it, does it eat? That's how you can tell. They might not eat if they are new to the surroundings - or more probable in this case - have a case of nitrite poisoning and are too sick to eat. Most damsels survive this cycle though, and that's why people use them. I have two dominoes just chillin in my QT tank, waiting for me to take them back to the store. They were in my community tank, and they are holy terrors. And, unless you get lucky, you have to take out a lot of your rocks to try catch 'em. Get rid of them while you can. They are cool looking, and have a cool swimming style, but if I had a billion gallon tank with a blue whale and a domino damsel, the damsel would probably harrass the blue whale to death. Take most people's advice and get rid of them after the cycle (take them back to LFS). It's not worth it if you ever want other fish.