Where'd that cloud come from...?

[ron101]

If you mean that your tank is a cloudy green color and the caulerpa is going white then it is going 'sexual'. Periodically it will release, for lack of a better word, spores for reproductive purposes.

When it happened to me I just cut it right back and eventually the skimmer cleared up the water. Supposedly regular prunings can keep the reproductive behavior in check but have not verified that personally.