Of my three the Hummu is the most peacful, and has never shown any sign of aggression besides when he's eating my hermits. The Undy is alone, and the Hummu is with the Niger, which is very aggressive. A more peacful Triggerfish would be the pinktail, blue-throat, sargassum, crosshatch, or Lei. While the list I just mentioned is a much better choice than the CT,Queen,BL,Undy etc. I've heard accounts of the peacful trigs getting medieval at times. My Hummu is a softy, I've seen them as terrors, and people complaining they've wiped out tanks, just depends on the individual. Nigers are supposed to be peacful? My near 8" Niger is an aggressive jerk, and bullies I think for the shear entertainment!