Favia died overnight?

[Pattheerin]

I had a favia that seemed to almost fully disintegrate the day after a water change. A few hours after the change I noticed it started to turn fuzzy and some of the outer base was falling off and floating away. Looking at it this morning, nearly all the other base is gone on one side.... what the heck could have happened?

 

[Copingwithpods]

Coral warfare? Was it in stinging distance of anything?