Need help fast!!!!!

[Edmonton Eskimo]

I have a 55 gal that was reef but I have changed it to fish and a couple corals(xenia and glove polyps) Everything has been great until I brought a small picasso trigger home yesterday. There has been no aggression at all from the trigger but I did have my red wrasse die last night but he had no signs of aggression either. This morning I notice all my fish are gasping for air. I immediatley tested my water and noticed an ammonia spike. Nothing that I could see other than a small piece of xenia that was dead. I have reduced the ammonia with water changes but nothing has changed. Is there any parasite that could have been introduced? I don't want to lose everything what can I do?