I would just cut some of the dead growth off. It really doesn't look like STN. My BN's sit in the top half of the tank under 250's

That could also be damage from something stinging it. Was there any neighbouring corals nearby, or could it have been tipped over into something?

Nothing near then at all. I have a flat rock that has hole's drilled into it for frag plug and they were in there away from everything else as they are at the top of the rock pile.

I'd have to agree with the advice to place it lower in the tank. I found that my birdsnests did their best growing at midlevel or at high level but slightly shaded (in other words that one was high, but it was also under a brace so it was shaded a bit). Too much light=burned

Sometimes these just go for no apparent reason too. I had one that was doing great for over a year and one day it a bunch of it just inexplicably died. *shrug*

Well I have put both BN frag's lower in the tank and it looks like they are doing better. I will have to watch them very close, Thanks to everyine who responded with idea's and help.

Strange, my tank has pretty much gone to shite, yet my pink birdsnest has stayed vibrant and keeps growing. Which is good, because I think this is the last of the colony that it came from about 5 years ago (thx Shao!)

It looks like too much flow to me.
I also agree with Laurier on the possibility of too much light too quickly after being introduced to a different system with different parameters than they came from originally. Hope it turns around for you though. :)