That is Sargassum , and no I finally lost my when the rio piump failed and almost kelled my tank, The Sargassum didn't survive for some reason, I think it will come back. It is cool, I did also find something that like to eat it, emerald crabs .
Tim , Sargassum will look like that over time when it matures and you lose the upper part of the plant. it almost looked like it is tryingto goe downward to develope root or something. Mine did that from time to time. I am pretty much a 100 % sure that is Sargassum grass.
alright - Sargassum grass it is then.....but it that bad. Can it either get out of control or conflict with corals at all? I'm not concerned with removing it from the tank unless it will be a problem towards maintaining a balanced tank.
It might be a Sargassum spp., but the overal morphology and growth characteristics just don't click for me, but then again, we are all shooting in the dark without a good photo of the entire thallus and blade forms, and a potential piece of the specimen in question. I tend to agree more with Timmah's last assessment, but then again, we're all shooting in the dark based on the quality of the photo. Keep in mind that Sargussum spp. are rapid growers and mature in a short season as pseudoperinneal algae, and although there are many morphological variatioins within an individual specie depending on wave action and current, that without good data on morphological variation of general habit, stipes, primary and secondary branches, primary and secondary blades, vesicles and receptacles, that we are proffering what should be considered just good guesses at WHAT the ID might actually be.
Sorry to burst the bubble for confirmation, but we really need much better photos.