Wow, that caulerpa grew really fast! You're going to have to manually prune that fairly often to keep in in check. Also, keep in mind that caulerpa has a tendency to go sexual, meaning that it will release it spores, turning your tank water the color of pea soup. Read through this article so you'll be abel to spot the warning signs of impending sporulation. http://reefkeeping.com/issues/2004-05/nftt/index.php