Metallic green hammer coral disappearing

Hello all. I have been stumped by my recent decline of my Metallic green hammer coral. It is 2 years old and was up to about 40 heads. Just this week heads are dying one by one. It does not look disease related as the base looks picked clean. No decline noticed in the health of the head but almost overnight I will loose another head. No changes in a year to livestock. Anyone else come across this? Any help would be appreciated. Sorry no pix - on my IPhone

180 dual overflow w/ AI Led's, vertex skimmer in sump.
Philstar 3 canister for carbon and Phosban w/ polishing pads.
Sohal tang, Yellow tang, Vlamingi tang, green chromis, firefish, perc and tomato clowns, cleaner shrimp, flame angel, orange cream/skunk clown, Sally light foot crab, usual reef clean up crew.
Multiple leathers, bubble, LPS and SPS
I feed marine pellets and just recently phyto for my ball sponge
My other hammer in a different spot has not been affected but it is not a green

Water test fine. Ph 8.2, calc 330, mag 1350, dkh 11.5, no readable no3 or po4

Thanks for any help provided

 

It seems your calcium is pretty low. I typically try to shoot for about 400 or even a little higher.

I know you said no livestock additions, but have you added anything new? The reason is that if it is disappearing one at a time, it sounds like something may be attacking it.

 

Any of your leathers nearby the fading hammer? Sounds a bit like it's under attack.

 

My hammer coral under attack

I concur something was attacking it, but not sure what. I fragged the healthy heads into a different spot and ended up discarding the main stalk because heads kept dying. I have a large toadstool and bubble in the area but think there is adequate space. I have not seen any issues with the 2 frag colonies I relocated yet. Thanks for the help. Time will tell