i have a blue hippo the is somewhat the boss of the tank, she does like to chase the other around and make them hide, with the other fish you have added to the tank did you acclimate them in a box in the tank? i do this with all my new fish so they get use to a new family member usually do well after a day or so. depends on how dominant he/she is, i dont think they will kill others though. usually with new fish they will sometimes hide and never come out because they keep getting chased back, even when feeding, then they will eventually die. like said the box has worked very well for me. if you need to borrow mine let me know.
I just looked in my tank and the Blue Hippo is gone. Maybe he is sick. I bought him from a guy that was tearing his tank down. I did see a hole in the side of his gill.