Seriatopora caliendrum on its way out. I've never seen anything like this before. I didn't take any photos of it yesterday but part of it was bleach white so I assume after the polyps swell up like that, the tissue just sloughs off to pollute the tank.
Nearby corals were unhappy as well:
As well, the polyps on my pink pocillipora damicornis and pink irridescent birdsnest are pulled in and they look pretty unhappy. I'm running new carbon and hopefully this doesn't progress any further.