Lychaete herpesticais commonly referred to as Filamentous Green Algae. Difficulty in the aquarium: Not suitable for aquarium keeping. Toxicity: Toxic hazard unknown.
www.reeflex.net
If not, I'd lean toward it being something else from that family (Cladophoraceae), as the bubble tubes are pretty unique - they're too long to be Valonia or similar, and too translucent to be Codium.
Thanks for that I started to think it might be a type of bubble because my new emerald crab has started eating it. I just added another after my old one had died off.