The Jardini is peacuful. He hasn't even touched one of my other fish yet.
This is comparable to pulling the pin out of a grenade, and not having it explode at the 5 second interval it is designed to explode at. Just because it took longer than 5 seconds does not mean that it isn't still a live grenade, and it should be treated as if it were, whether or not it ever actually explodes.
Even if the fish grows to its full size in 5 years, and hasn't attacked anything in those 5 years, doesn't mean that it will never choose to do so. It is the simple fact that it posesses the ability to kill anything in that tank which should make you reconsider its living arrangements. Granted that we've already discussed the fact that it cannot live its whole life in a 125g tank, you will likely want to be looking into funding and placement ideas for a 240+ gallon tank VERY soon, for the sake of being precautious and protecting your other livestock. You can house a lion with a chicken and have the two co-exist for a while, assuming you keep the lion well fed... but as soon as that lion gets hungry or bored... the chicken will cease to exist.