rusty coraline?

[Myka]

Coralline can get what is called CLOD or Coralline Lethal Orange Disease, and you have photographed a great example unfortunately. Resources say it is caused by an "unknown bacterial pathogen". I know of no cure and as far as I know, neither does anyone else. Scientists are researching it though as it threatens the world's reefs. It doesn't cause nearly as much damage in our reefs though as our tanks don't need coralline to hold it all together, albeit looks rather nice.

http://findarticles.com/p/articles/m...6/ai_15811426/