How big was the new tank? I assume it was the tank size that made the difference. I've found and reported the same (above) when I rehomed mine from 240 gal to 4500 gal. Mine had gone from horror to a model citizen.... the artc was a little over 24'' when we finally decided to try him with the other large cats ,rtcs,shovelnose , marble achara, other notable tank mates where alligator gars and a pima, shortly after adding him to a tank with larger tank mates the aggression was gone just like that no rhyme or reason just gone...