ID please - Macroalgae or?

[stevebydac]

Hi all, does anyone know what this is? It popped up suddenly next to a couple of small zoa plugs in approx 150 PAR. When small I thought it was some sort of rogue mushroom, but as it has grown perhaps it might be some sort of macroalgae? It is growing quickly, doubling in size in 2 weeks. The 2nd photo shows a clump of it hijacked by my tuxedo urchin.

I've seen these links, but not sure:
Porphyra leucosticta

https://www.saltcorner.com/AquariumLibrary/browsespecies.php?CritterID=2104

"specimen of a Rhodophyte... likely a Fauchea species"

RedAlgIDFAQ2

http://wetwebmedia.com/Algae%20and%20Plt%20Pix/Red%20Algae/redalge%20idwwm.jpeg

Parameters are pretty good for an LPS tank, steady in the following ranges:
PH 8.1
Alk 7.4-8.0
Cal 420
Mag 1350
Nit 10-15
Phos .04-.09
Sal 1.0255

Thanks for any thoughts.