I am housing my friends Black Belt for him right now. When I first got it, it was beating up all the fish in my 125 within two days. I then relocated it to one of my smaller tanks for awhile so that it didn't go on and kill any of my fish. I just put it back in my 125 two days ago and within 24 hours my RTM, JD, and buddies Dovii that I am also housing have almost killed it.