I’d help of purple growth.

[David]

This was an acro frag, that withered away and died in my previous tank. I put it up in the light in my new tank, and it grew this bright purple growth out of the base. It’s growing quite fast. The acro showed no signs of life for at least 6 months in the previous tank.

 

[Mark Shelly]

there is a purple hair algae, although the lighting may be contributing to the purple look.

 

[David]

Hmm. Ok. Not an exact match, but possible. I have no nuisance algae problems so far.