What's going on here

[MadReefer]

Noticed this dark color on my yellow scroll. It just started coloring up in new tank. Looks like a crack but its hard. Should I be concerned?

 

[DangerDave]

I can’t really tell from the pic, but it kinda looks like it receded and something is growing on it. Can you get a better pic?

 

[MadReefer]

It's hard stuff growing. Doing a peroxide dip today as I bought some coral at ReefCo.

 

[MadReefer]

Best I can get during peroxide dip.

 

[DEL]

I had the same years ago when I had a scroll/cup coral. I was told break off the piece because it can infect the rest.

 

[MadReefer]

I brushed it with a tooth brush and looks like a type of algae.
Will see how it goes.

 

[DangerDave]

I’d be more interested in trying to figure it out what was causing the recession than the algae...