As I understand it, Caulerpa goes “sexual” by releasing gametes into the water column, along with other nutrients. This lowers the pH of a tank as well as the O2 levels as it pollutes the tank with these gametes. In addition, these gametes can attach themselves to rocks inside the aquarium and begin growing there. So aside from the low O2 / pH issues, there is the potential of having a bloom of Caulerpa in the main system.

Charley