that's what i thought, but someone else had a picture just like mine and they told him it was cyano. i kept doubting myself and still am. but from what ive seen happen on my other rock, it turned red, then purple coraline grew over it? ive been keeping my calcium at 400+ppm, with a dKH of 8-9, magnesium 1300. not new to the hobby just never really paid attention to coraline. its always been about the health of the livestock. this stuff seems to be invasive on the rock only, and only parts that were brown, and not any corals or existing purple coraline. just by that i can only assume it might be coraline | 
