You might give Marine Algaefix a try. I've read on some forums that some people have used it to eradicate caulerpa with success.

I've never used it but a friend of mine who does service has been using it on his service tanks (fowlr & reefs) for awhile now with no harm to any fish/invertes/corals. He says it works great on all green algae (hair, bryopsis, etc.) as well as diatoms. The only negative that he has seen is a small cyano bloom from the released nutrients when the green algae dies off. Like I said, I haven't personally used it (no sw tanks at the moment) but he sold me my first coral in the early 80's so I trust his opinion/experience.