I would imagine the size of the tang, and quantity would make a big difference in the size of the QT. I qt 1 - 2.5" pt, 1- 6" dfpuffer, 2 - 3" tomatoe clowns, 1- 5"antinatta lion, 1 - 6" marine betta in 20g.long with no problems until one of them decided to try and kill the betta. Once the betta was removed all was well again. They were qt for 8 weeks.
LOL, Marrone beat me to it.