Favia frag bleached spot?!

[NanaReefer]

No idea why. Especially since the frag right next to it shows nothing of the kind. Nor anything else in the tank for that matter.
What could be that cause and how do I treat/stop it?

 

[KorL]

What lighting are they under?

 

[Camellia]

Do you remember something falling on top of it? Looks like it got stung.

 

[NanaReefer]

It hasn't been stung. Nothing fell on it. It like all others are under 180w LED's. 20/50% max. Ramping up/down for 8hrs. Whites on for only 5hrs.

 

[J Rog]

possibly to much flow? Maybe the first to react to an alk problem?