Hi Jasper, congratulations on the addition of one cool coral! Everytime I talk to my LFS about my dendros they think I'm saying Dendronephthia as well...hehe...
Dendrophyllia are non-photosynthetic, but they can tolerate and thrive in very hight light areas. I bought mine from The Captive Reef and he keeps them inches under his halide, not because they need it, but because that's the easiest spot for him to reach for feeding. What matters the most to them is feeding often. The food they seem to prefer is raw squid; if yours ever stops extending its tentacles this food usually pulls a stressed out one through its funk. I feed a variety of small chunks of raw meaty seafoods. Finely chopped scallops, prawns, calamari steak, and mysis shrimp. Just make sure you give it no less than 3 x a wk, and if you want fast growth and constant tentacles on display, at least once a day (on the weekends I continually feed mine every 2-3 hrs, but on weekdays I can only get in a morning feeding).
Flow should be Medium. Not blasting, but present enough to sway the tenacles gently and flush away wastes.
One other thing, they CANNOT tolerate contact with soft corals, so if you have any be sure to give it a wide berth. The only problem I've ever had with mine was a zoa frag dropping on it in the night; next AM tissue necrosis in the dendro. My stinkin' zoas pulled through just fine! I know someone else whose Yuma expanded so large during the day while he was at work that it was stinging his dendros, but at night when he got home it was shrunk enough that he couldn't figure out why his poor dendro was dying for about a week. He thought there was plenty of room, but not in the height of the Yuma's daytime happiness.
Any pictures?