^ +1.
Tank size isn't an issue for most of the fish you could want to keep with a silver provided the tank is big enough for the silver. (it makes me laugh and cringe at the same time, my interest in the aro forum here waxes and wanes, I won't check it for months and then start reading it again, and every time I come back Brian is still here trying to explain to people why you can't keep a 3' fish in a 180g tank...)
Generally speaking, if its big enough to not be eaten, and not so aggressive it will beat on the aro, and not so big it will eat the aro then you can keep it with a silver............
To be honest it's rife everywhere; you need only think of a large fish of some description and someone will be trying to keep it in a tiny tank and will still have the ordacity to get up in arms when someone tells them they're wrong. Best bet is to try not to get annoyed by it...!
But, in answer to the question, while I don't pretend to be an expert in Arowana specifically, like with any aggressive/large fish, give them enough room and generally, you don't see too many issues. Not that that helps you, since your tank is too small.