yeah, i have had this problem.
knives and arowanas cans ometimes not like each other.
maybe cos they are both bony tongue, same shape around about.
but i had exactly same problem with my rtg.
they wre ok, and when i moved, suddenly rtg snapped and kept on harassing it.
simple fix i reckon.
drift wood may hurt your aro but definately h elps. but whats gonna happen, well happened to me is that the knife WILL never get out, as it does, aro will chase it.
what id id was introduce a oscar in there.
oscars are robust, and will eat in any condition.
also i added the tinfoil barbs...
the distraction was enough to stop the arowana.
if that doesnt work, maybe send it to anger management school - as the crusaders who they send their players to:D