algae ?

[hobbit]

growing in reef/coral 24 gal nano-cube...sending out long tendrils ( 3" ) with fern like sprouts---bright green color


wat is it ?

[Randall_James]

[welcome]
With that out of the way:

pictures are pretty much required for ID in most cases as many things are subject to viewer perception and there are lots of things that look alike.

[Steven Pro]

Just a wild guess, but it kind of sounds like Bryopsis. But, a picture would be helpful.