One of the downfalls of using Caulerpa in a closed system is that the colony can ?go asexual?. There are many reasons for this to occur including stripping the system of all dissolved organics. One suggestion found to help override the asexual process is to run lighting twenty-four hours a day seven days a week. As well prune the alga back frequently which will completely remove the nutrients from the system and will encourage new growth. I have never had any Caulerpa go asexual thus far so I really can't comment on it. People I have spoken to about it state that, the water goes white and the oxygen levels in the system will lower endangering animals. In this situation the best solution would be to do add carbon aggressively and do a large water change.
thanks for the responce , the reason i ask i have caulerpa in my refugium and im running the lights 12 hrs. So far every thing is good, system is been running for a year. In your opinion should i change to chaeto?