Sinularia coral if I had to guess from that photo. I have the neon green variant. They are a very easy to care for coral. A rapid grower. My angelfish eat them.
They are easy to control. They do get big and will need pruning on occasion. I just reach in with scissors and cut off a few branches above the base and with an elastic band, strap them to a rock and place in a low flow area. Within two weeks they are attached and ready to give away. New branches will grow from the cut on the mother colony.