I have had this cory for a week. Everything was fine up until about 2 days ago I would think. While checking on my fish this morning, I noticed that one of my cory had what appears to be white fungus on one eye. Upon further inspection, it appears has if his head was crushed. Kind of like when you break an egg shell. I have never seen this. Water is good with no ammonia or nitrite. No aggressive fish that could have done this to it. I can only think that he came sick from the store. Is there anything I can do to save it?