People like to label jardini as "killer." Jardini is just an arowana like any other arowana. Unfortunately, they get branded by incompetent individual, who can't accept his mistake, rather blame it on the fish
To OP, the only problem with keeping an 8" Jardini with an 8" ray is that there's a slight chance the Jardini becomes ray food. Also, there's a chance the Jardini goes after the tatf. That silverish darting little fish can be quite annoying, oh and the tatf can also become ray food