IME they simply won't last. I tried two types, both perished over the course of several months. I would identify which type they have and ask Dr Ron on RC in his forum for help. I also noticed NewReeferLady has some, but I don't know for how long.
It depends on the type of tunicate. Some are low light low flow, some are high light medium flow. Any more information on the type? The scientific name would be great, but a real good description would also help.