What's going on with this coral

[DISC0]

I have a birds nest that has been doing great for a few months. When feeding the tank today I noticed this and am unsure what could be causing it. And how I can correct it.
Anyone have any ideas.

Tank Paramus are
1.25 SAlinity
Ammonia, trite, and trate at 0
Alk 12
Calc 420
Ph 8.0-8.1 depending on time of day or night

Thanks for the help

 

[afamousjohnson]

What is in bottom right corner on pic? Could be getting stung?

 

[DISC0]

It is a brain coral.

 

[DISC0]

Here is another picture.

 

[afamousjohnson]

Are there polyps below the white at the base?

 

[DISC0]

No but it is not bleach white like the center section there.

 

[afamousjohnson]

If it continues to move up the coral you may have to frag off healthy parts in order to save it.