It looks like grape algae, it grows very quickly if not controlled. even the smallest piece will grow quickly, so keep it under control.it makes a great phosphate export.
It's a Caulerpa species. Depending on what you want your tank to look like, it can be either good or bad. Lots of awesome planted tanks out there, and I just converted a 90G to one. It can be tough to control if you want it out. The rhizome will sprout from any piece of it left behind. Again, good or bad depending on what you're after. I would be more concerned about the hair algae on the left though.
i take it from all the great feed back that i can leave it in but just keep it under control.as far as the hair algae i keep trying to remove it by hand . it hard cause its right next to a power head and deep behind the rock.open to any suggestion that anyone may have.
Yeah. Leave that caulerpa in because it will utilize the nutrients that the hair algae uses and it will look cooler. So the hair algae may get starved. Then you can get a tang if it ever gets to be too much, because tangs eat it like candy.
save your hands and dont bother trying to remove it. you need to treat the source not the symptoms.
here is one that still has me puzzle about 2 months ago i lost my yellow tang then followed by my purple 3 days later. no signs that i can detect ,lost no other fish.