Most wild caught fish we buy that die a month after we get them, die from an intestinal upset that is the end result of shipping and drug treatment. Durgs are not only used to cathc them, but are used along the way at each stop along with diluted water. It masks serious problems and creates some. Having a fish for a month does not mean its healthy and an active angel can be sick as a dog and on the verge of death. If you can prove it didn't have something wrong with it, then look around in holes in your live rock at night for a club anemone. They live in the dark and will kill anything that runs into them. Its better to buy an angel that is not actively swimming up and down, to and fro, but rather one that is searching for things to eat on a rock and a little more shy.