hey kris, tons of caulepa can be kept in your main tank, it just requires an occasional pruning. for exapmle, i have sawblade caulerpa, feather caulerpa, grape caulerpa, and one other type groeign in my 20. it looks very cool, but needs to be "pruned" form time to time. caulerpa also helps out by oxygenating the water in the tank, pulling organics out of the water, and competign with pest algaes for nutrients and space!
good luck
jon