I'm not sure how good a job they'd do on caulerpa, since I think they mainly eat hair algae. I've seen them in tanks with caulerpa and they didn't touch a thing in there, probably ended up starving to death. The ink isn't that toxic if the tank is over 30 gallons or so, in my opinion, and some carbon will clean it out really quickly if it's a problem. The only thing I've seen that eats macros heavily is a scribbled rabbitfish, but they like to have some roaming space
Also, if you're going to sell the caulerpa on ebay, make sure you add something about not shipping to cali (and some other states probably) since it's illegal from freakin people flushing them and it ending up in the ocean