Please help. Hammer coral deterioration

[Reef_dachs]

Hi,
I have a branching hammer coral that was beautiful 2 days ago. There are 4 heads on this branch and the top 2 heads are quickly deteriorating. I’m at a total loss here. Everything else in the tank is good.

Temp 77.7
Salinity 1.026
Nitrate 5ppm
Nitrite 0
Ca 460
KH 12.6
Phosphate .03
Ammonia <0.15
I have attached a before, 2 current pics and an overall tank pic

 

[Shefilbel7]

Is the KH always 12.6? Or has that increased recently?

 

[Reef_dachs]

It is usually between 10-12. I did a water change yesterday and it usually rises a bit afterwards.