How to stop an encrusting coral?

[Phormium]

Thanks all for the suggestions. Unfortunately rock removal isn't possible, the mystic is running out from a rock central to supporting the main rock tower in my tank. It would really destroy the landscape I love by breaking apart that tower. Figures.
So I think I may try shading some of it which would place it into near darkness, I have chipped some of it away, and I may be able to cover some of it by gluing rubble on top. It might recolonize but it will give me some time. Might also try the glue...