What's This?

[showey]

Okay, Still having trouble figuring this out. Can someone tell me what this is? Came on the LR that I rescued from a guy that had to move. Is this good? Bad?
cut it or keep it?

 

[Random Aquarist]

Looks like the stuff on MarineLife.com (Actinotrichia fragilis).

 

[piercho]

OK well thats a new one for me. Is it calcified (feels hard and brittle)??? If it is calcified search around in the genus Jania and Amphiroa. If its not calcified maybe Ceramium. That's the best I can do without better cues (and keys).

Since it appears to grow up from a single holdfast its unlikely, IMO, to become a problem. Most 'problem' algae are creepers (Caulerpa), filamentous detritous trappers(Derbesia), or aggresive sexual speaders (Ventricaria). Algae like Sargassum which don't spread readily by fragmentation or sexual reproduction and grow up from a single holdfast are generally desirable nutrient controls, IME.

 

[showey]

It is not calcified and IS flexable. Coralline algae is starting to form on some of the branches but other than that it feels like a plant.