Right now they're in a 55gal. I want to move them in a 150 by december. My butti is about 4in long but he's tall and wide and it makes him look bigger, he's aggressive but he doesn't give me any problems. If he ever outgrows my syn then we may have issues but as of right now he just likes to swim, eat, look pretty, and occasionally challenge the Syn. The Syn is about 6 inches and is the boss between the two. I love him to death, he's so much fun watch and coloring up nicely. I'm gonna get him some better food to help enhance his color.