I doubt the Torch was able to sting it all the around like that. I don't think it's your nitrates either. By process of elimination I guess I would have to go with a disease of some sort. Which one, I have no clue. This might sound a little extreme, but if the corals condition doesn't improve you could always just lop the top off. I do this to mine about once every year or so and it always grows back. Definitely something to consider. GL.