I had to remove a Chromis a few days ago. I started with seven and now I'm down to two. There seems to be a pattern. First, the poor fish hides for between four to six weeks, barely venturing out for food. With the last one someone took a huge bite out of it's back. Then the fins get shreaded. I finally found the last one looking very weak, and I was able to easily just pick it out with a net. It didn't even bother trying to escape the net.
Only one way to find out about the accuracy, and that's to get an ICP test to see if it matches up.