birdsnest dying?

Are there still Polyps on the white part?
Do you have any pictures?

I once had an event in my tank where my birds nests and montiporas started turning white at the base, within a week they were decimated. All other acros were fine.

I was told this could be a low magnesium issue.

I've had others start dying off when they get really big and light and or flow doesn't reach the inside of the colony.

 

His staghorn's base turned white because of high nitrates

 

Could be many different things. If it's dying or is dead i would start looking at high nitrates, Ammonia, high alk or a combination.

 

Is it green birdsnest? Saratapora guttatus?