Vivid's Halo Branching Hammer CoralHow to Care for Vivid's Halo Branching Hammer Coral: (written by Dave Burr) Vivid's Halo Branching Hammer Coral is a great beginner coral and will sway back and forth to the currents in the aquarium. Hammer Corals are a favorite of many because of the sense of motion they bring to a reef tank. Tentacles: They do have sweeper tentacles that can extend 2" 4" at night and sting nearby corals. Hammer Corals may be placed next to other Euphyllia species