Could be Dictyota, but it looks like a harmless macro. Maybe!
I agree with Webmanny. I would hold off taking action until someone identifies the type of macro algae.
That looks like a slow growing algae IME. I'm no expert but I had that in my tank for a while. Didn't do any damage, went away on its own once my tank got more mature.
Over months. I just noticed it was gone. I didn't mind it and did nothing to get rid if it. I think it was one of those many things that take care of themselves once the phosphates and nitrates are under control and the tank has more stability.
Personally, I liked the look of the stuff.
Now, caulerpa - my experience with THAT was not good! I finally threw out the rocks it had infested. (After it went sexual, smoking up the tank.) No crash, but I was nervous.
Good luck with whatever you decide to do or not do with this algae.
Michelle
It is almost surely a species of dictyota, most likely dictyoa dichotoma.
Some people like the look of it, some people hate it because it can be invasive and a pain to get rid of considering that very few things eat it. It can also grow in relatively clean water so it might be very difficult to "starve" into submission.
If you try to remove some of it manually, be sure to take the rock out of the tank first.Otherwise any loose pieces will just colonize other spots in the tank.
If its big enough to pull off and you don't want it, depending on your location I'll take it
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