Dying Corals

[Jaws]

I'm not sure what's going on with my tank lately. I've lost four really nice colonies that I bought from yifan917. My parameters are good too. I don't understand it. All of the frags I got from Ocean aquatics are alive and well. I lost two of the colonies over the last couple days and then two of the frags (one from Brad and one from Ocean Aquatics) that were close to the colonies died too. Is this normal?