Thats tissue necrosis, you can see it more clearly in the second shot. Not much you can do really other than either watch it closely or try to frag it and perhaps crazy glue the affected bits at the bottom to try to seal the tissue. It sort of looks like the tissue is thinning at bit at the top of the colony as well as the tips look like they've got some algae on them perhaps due to rubbing the sides of the transport bag or something.
Is it a new addition? You've had it awhile? It does look a bit "rough".
I'd put it down as low as you can in the tank in some medium flow area. Hopefully it will recover.
Good luck
