I have one. I've only had it a few months. They do not need light, they have no phyto living inside their tissue. In nature they are found in caves, near total darkness as well as in high light areas. I have mine in a high flow area, glued so it hangs upside down (It is in bright light I guess). The polyps are white tentacles with a tiny yellow center, and extend nicely at night about an hour before lights out, this is when I feed. I have heard that phyto is not enough for them, they are heavy feeders. I pulverize brine, and other foods up current from them, and let the tiny particles wash over it when the polyps are out. I've been thinking about maybe some kent invert food, and target feeding it with a pipette when the poyps come out, but so far so good with the method I've been using. Hard to say if it has grown. It inflates and deflates daily. It has not shrunk as far as I can tell.
Jury is still out on how well they do. Some have good experiences, others don't. As far as additives go, I don't know if they have specific needs. I add iodine occasionaly and keep my ph and alk levels up and calcium is 480.