10 months is a good age to add more delicate fish such as angels,butterflies,and tangs.
You are right about fish such as the flame being sensitive to Copper.Tangs especially...and puffers can't handle it at all.It causes damage to their internal organs,and in some cases kidney failure.
Tizzo,the most prevalent problem with flame angels,and also yellow tangs, is their capture method,ie:cyanide.
By the time you get them{several weeks after capture},is about the time the damage that has been done manifests itself in the death of the fish.
Look for stores who try to deal with wholesalers that buy from suppliers who don't buy from those who use cyanide to capture fish.
Avoid the "brightest" fish..in this case often a sign of poisoning.