I have about a 22inch Jardini arrow and hes super mean. Maybe I just have a guy with a an attitude, but I don't see how the discus would make it long at all. when he was 15inchs or so he killed large hand size tinfoils, at 18inchs he tried to kill 2 blue channel cats that were about the same size... The cats would just hang out on the bottom in a tube or something and he would just go down and bite the crap out of them leaving them scared and bleeding, around the same time he also decide the other tank mate an Oscar was time to go.. He now tries to eat my 90pound dog threw the glass every time the do walk by. He will also bite at the glass if I hold his thawed shrimp in front of the glass, taunting him.