Zoa wont die but rot or melt away. Some may take a while to acclimatisate bef opening but should not be more than a day or two. Maybe u can take out and dip them to see whether any parasite like nudi. For your hammer... Were they opening fully when u purchase? So far.. When they start to behave this way... Likely gone case. Cutting those affected is in hope to stop the spread. Not 100 percent but at least try. In the forum, some sellers... Buy and sell to profit... So got to be careful especially buying corals does not equate to 100 percent survival rates... Seller can always claim is Yr tank, the way u handle, acclimatisation, etc. So be careful.