I have a school of 8 tiger barbs in my 55 w/ xray pistia, serpeas, black skirt tetras, danios, bn pleco, cories, loaches & SAE's and have not had any problems. They quarrel amongst themselves and I haven't seen them *go after* anybody. Prior they were in a 26 gallon by themselves. I was hesitant to put them in but it's been a month and so far so good. Besides the cories, loaches, danios and bn pleco...all the other fish have their own strong personalities and I'm sure they would nip any slower, peaceful species. I love my tiger barbs and I'm glad they are in the 55 now. They do add a lot of flair!