Favia not doing well

[Silverni2]

I can't stop my favia from depleting. Over the past month my favia has been slowly dying, I've done countless water changes but can't figure out why. I've had it for 3 years.
The biggest change I've made over the past 8-10 weeks is add carbon to the tank.
My Ca 420 ish
Alk 9 ish
Mag 1400
Nitrates between 3- 5
Phosphates 0 Elos test kit
My other corals have been slightly effected by the addition of a good carbon but none have continued to deplete or die.

 

[Jan]

Looks like White Band Disease or Black Band Disease.

Do a search for White Band Disease/WBD. It's caused by several strains of bacteria. Do a search for various treatments. Good luck.

 

[Nic-reefs]

Did you try to dip it

 

[Silverni2]

Did you try to dip it

I can't get it out of the tank it's attached itself to so many rocks that I would have to rip apart half the tank.