The fact that the new Angelfish was subsequently recaptured tells me that it's very stressed right now and possibly weak. This is a great time to use Garlic Oil in feedings because stress can lead to Ich.
It's just my opinion but those acclimation boxes placed at the top of the tank can be stressful on the fish because it places the fish in open top water and bright light. Reef fish do not live in that zone. I recommend using a clear quart size or larger container with a small LR to hold it down on the bottom of the tank, with macroalgae for cover and for nibbling. The lid is replaced with bridal veil material held on with an elastic to allow free flow of water. Watch all the fishes for aggressive displays toward the newcomer and use a stick to train them.
Fish are more intelligent than commonly assumed. Training a fish can take from 30 minutes to 24 hours depending on the fish, and sometimes, even after this the two fish may have mock battles for a week or two. Keep the stick handy to discipline the misbehaving one. It's not cruel. The stick rarely makes contact, but it can be used to chase the fish a little, to show the fish that you are the boss of your tank. In the world of animal training, it's called "conditioning".
Before adding a new fish, the tank can be prepared by overfeeding for several days. Overfeeding after introduction also helps, since aggression can be 90% related to the old fish thinking there's not enough food in its environment for the two of them. That's where it really helps to encourage natural food growth in the tank, in this case soft surface algae, prior to introduction.
Of course all this info, and more, is contained in threads linked in the Reefkeeping Tips. Have you referred to those Tips when you have questions?
Aloha,
Mark
Edited by Mark Peterson - May 23 2016 at 10:26am