Dying Brain?

[Kryten]

I bought this green open brain coral like a year ago or so. It had a small damaged spot when I got it that I hoped would heal up. Well, it stayed the same for many months, but now in the last month or two has been getting bigger. And I noticed that lately my sexy shrimp has been sitting and picking at the dead/dying edge of it. Is there anything I can do to reverse this or at least stop it? I only have it under pc lighting, but my candycane coral has been doing fine under this, quadrupled in size in the last year. I don't do any supplementation except for a bit of liquid calcium supplement and regular water changes.