Not sure what's wrong with my Duncan Coral...

[Og Drogon]

Native to the deeper waters of Western and Northern Australia and the South China Sea, this coral prefers to attach to solid objects in soft, sandy areas. Here, they readily propagate and often form a continuous mat of tentacles that conceal the overall shape of the underlying colony. In the home aquarium, place in low current areas with low to moderate light.
This is just from :
Liveaquariea.com

Fix Your Fin Or Get Your Fin Fixed!