ID plant or sponge?

[Etszoo]

 

[ISpeakForTheSeas]

I'm going to guess a sponge. Do you have any pics of it under white light?

 

[vetteguy53081]

This looks like a macro algae known as Grinnellia but may also be Fauchea.
It is related to a rare macro known as porphyra leucosticta

 

[WheatToast]

This looks like a macro algae known as Grinnellia but may also be Fauchea.
It is related to a rare macro known as porphyra leucosticta

Not sure if it's Gracilaria or Fauchea (Gloiocladia) since these feature finer branching, though it's definitely some red macroalgae. Might also be Halymenia (ex. Halymenia floridana), which appears more commonly in the trade than Porphyra; the former is highly palatable to herbivores and I would assume the same goes for the latter.
Information:
https://www.marineplantbook.com/marineplantbookredalgae.htm
https://gulfspecimen.org/specimen/marine-plants/marine-algae/

Do you have any pics of it under white light?

+1

 

[Etszoo]

I will try to get a better photo when I get home. It's at the top of my overflow. Clearly it likes a lot of flow.