Sick soft coral

[TTTony]

Not sure what’s wrong with this I’ve had it for many many years continues to spread only recently it has changed color turning black, I try to siphon off some of that and it’s just clear underneath it’s the only thing in the tank not doing well

I also have two of these in two different spots in the tank one is completely healthy

 

[Rainblood]

Is it being stung by another coral?

 

[TTTony]

Is it being stung by another coral?

No it’s been in the same spot for the last year and a half and recently started growing stronger, I did however add a large large zebra moray to the tank but the water parameters are reading fine