First I have heard of this! Did you read this somewhere? if so can you provide a link as I would like to know.
So what makes a good or "best" algae for nutrient exporting refugiums? Besides being fast-growing and stable, it must also be non-aggressive. On this point, we have learned some painful lessons through the years about the genus Caulerpa. You will hear some aquarists say that Caulerpa is the best algae for refugiums, and you will find many others that say it is the worst! How can there be such a great difference of opinion? I will tell you that both are correct. In the hands of a knowledgeable aquarist that understands the needs and dangers of Caulerpa, it can be a wonderful boon. But in the hands of the unprepared and newer aquarists, it may eventually become a disaster. Although I truly admire the beauty and effectiveness of the genus Caulerpa as decor and as a vehicle for nutrient export, I rarely recommend that it be cultured in large quantities. It's just too dangerous.
One of the biggest complaints about Caulerpa is that it is prone to sudden die-offs from stress or sexual reproduction. So many of the undesirable elements that it had absorbed into its great mass in the days and weeks prior get suddenly purged into the water during these massive, vegetative events. The shock is too great for many organisms, and aquarists have reported some catastrophic losses of display creatures after such events. Beyond any issues of toxins released, though, there is the simple fact that several kilograms of vegetable matter (the dying Caulerpa colony) are rapidly decaying in the system. The sudden proliferation of bacteria and simultaneous increase in demand for oxygen (bacterial bloom) on the decomposing colony is enough to stress or kill aquarium fishes. Ironically, this dramatic and potentially devastating disadvantage to Caulerpa is easily avoided!
There are two ways to generally reduce vegetative die-offs of Caulerpa: 1) keep it in stasis, or 2) interrupt its life cycle with strategic pruning. On the former count, "stasis" is "in layman's terms" a state whereby the Caulerpa does not get to complete its life cycle by keeping it under constant illumination (as recommended by some advocates of the mud system refugiums keepers). In practical hobby applications, Caulerpa is one of the only algae species that this can be applied to. The majority of plants and algae must have a period of respiration (day/night photoperiods). Speaking to the latter possibility for staving off die-offs, one can simply interrupt the cycle of maturity by frequent and aggressive thinning or pruning. Thinning is best as Caulerpa fronds are single cells (the largest single-celled organisms on the planet, as I recall), to cut or break a frond itself can lead to sapping of the entire cell (releasing noxious or toxic elements), or even a complete and rapid die-off of the entire colony! A patch of Caulerpa though will naturally grow many, branching fronds which naturally break and separate on their own. Take note of the older growth and thin it out of the bunch. This is best done habitually on a weekly basis with fast growth, but no longer than monthly ideally. The natural life cycle of most species of Caulerpa falls within three to six months. The goal here is to interrupt that cycle to prevent sexual reproduction and massive die-off.