Right now, my jar is only about 5.5 inches. It is living with a 2" black skirt tetra, 3" blue gourami, 3" gold gourami, 5.5" senegal, 5.5" marbled goby. I haven't had any problem with any tankmates except my 6.5" tat. When I first put the tat in with it, the aro was afraid of it, but the last 2 times I tried removing the divider, the jar hit the tat and tried to kill it. It's probably because the tat is silver, but it hasn't killed the tetra, which has a lot of silver.