Ditto what Scott said, although I never had trouble lighting mine 24/7. After a few weeks, the bugs all seem to get used to the sun never setting. Whatever you decide, just make sure the light from the refugium doesn't interrupt the night cycle on the main tank (since they'll prolly be pretty close to one another).
Caulerpa's are good in that they grow fast, but some people seem to have trouble w/ them going sexual on them. When that happens the plant releases gamete's, turns to mush, and generally pollutes your tank. In small doses I think it's beneficial, if your whole colony does it, it can get pretty ugly. For that reason, a lot of folks will tell you to shy away from Caulerpa's. Halimeda doesn't suffer from this problem (it will go sexual, but doesn't add a lot of pollution to your tank when it does), however it grows very slow, and eats up calcium and Alkalinity. If you're growing algae for nutrient export, this one ain't the best choice (although I think it looks better than Caulerpa).
The best one I've found for refugium use is "Maiden's Hair Algae" being sold at a few MO places and around the internet. It's soft and green, and I think a caulerpa species, however it doesn't attach to the rockwork and grow roots and stolon's like most Caulerpa's (making it a huge PIA to clean out), has never gone sexual on me, and grows like a weed. It reminds me of Green Angel Hair Pasta, or a Brill-O pad. Great stuff. If I were to setup a new refugium now, I would use a mix of Halimeda and this stuff, and avoid the other caulerpa's. Not that I have any problems w/ them, it's just that compared to the maiden's hair, they're all a PIA.
- Mac
