I have a 55 gal tank, and I have 5 Serpae tetras. I have not had any issues with them. In my tank along with the serpae tetras I have 2blue gourami's, 2 sunset gourami's, 6 tiger barbs, 5 angel fish, 3 different types of cory catfish, pictus catfish, some small algea eaters, and red tail shark...