Candycane corals bleached?

[AndyNguyen92]

I have a problem with a bulk of candycane corals now. The whole one grew just fine. But a week recently, my corals started to bleached gradually from the small spot center, now it is spreading out.
anyone knows this symtom? It die one by one of the branches
The dark area was those bleached when i took it under moonlight, and the brown area are those I took with daylight.

 

[Shep]

Hmm have you changed anything at all in the tank?

 

[Tahoe61]

I see tissue recession which makes me think chemistry.

Also the coral is larger, is flow impeded?

 

[AndyNguyen92]

My tank has 4 flows attached which are 2 1500gph and others are 850gph while other corals are just fine
I would begin to think that caused by my fish which i just introduced a black and white heniochus butterfly fish. Is it possible?

 

[Purple Platapus]

Is this a new addition or has it been in your tank for a long time already? I made the mistake of bleaching some candy canes by adding them without acclimating them to my lights.