What the heck is this??!!

[Reef Pilot]

So, what type of conditions and trace elements do these red algae prefer? My tank recently went through a phosphate spike (when I combined sumps with another tank that had higher phosphates). But that is getting back to near zero now. My nitrates remain at zero (or undetectable). And I should add that it is an SPS dominant tank.

I have not added any live rock (just some dry marco rock), and the tank is about 13 years old. I have no idea where the live rock originally came from (we bought the house 3 1/2 years ago with the tank running).

So just wondering where this red algae came from? I have never seen it before.