definitely coraline.
First, it'll be that bright green.
Then it'll progress to a light purple,
into a Deep, dark purple.
Sometimes after that you'll get a real intense pink. My tanks are just now starting to get that. And they have been set up for a long time.
What about the small rocks? Are you saying you don't know why you put them in that small area? Is that a back chamber or a sump or something?
That's okay. It's good. That will be more live rock for you to hold micro critters, areas for extra bioload processing, without crowding the Display tank. It's "Live Rock Rubble" and a lot of people do that. That way, you have more room in the DT for more/bigger fish, but that same amount of LR in the tank.
It's a smart idea, IMO.
I dk if it matters what chamber of the sump it's in... someone might chime in and say that one area is better than another.
Lookin' good.
Ps I now see it's a sump.