I've never had long-term success with caulerpa Mexicana. I've had it to flourish to the point that I was having to remove handfuls of it from my refugium, only to wither away to nothing in a matter of days. I've tried to grow it on several occasions, always with the same end result. I think it does well as long as there's an abundant food source, ie: nitrate, but once the level drops, it dies off. I have tried several varieties of macros, and the only one I have long-term success with is chaeto. I have a 30 gallon tub of saltwater from a water change, and the chaeto I harvest gets thrown into this tub (I hate to throw it away). I now have about half a tub of chaeto. It doesn't seem to mind that it's not lit up, nor has a fresh source of nutrients. It just sits there all green and pretty. It's the hardiest of all macros in my opinion...