Johny, hi.. that is quite a big tank for two 6 inch arowanas.. like brian and the others commenting adding more arowanas could work both ways.. I would suggest you give it a couple more days.. try adding some(not to cover the whole surface but say some 50% of the top) floating plants and extra cover so they can avoid any sort of eye contact.. what are you feeding them btw and enough? aro domination / aggression from what i've read and heard is primarily cos they are top feeders, they look for food and tend to think another aro is competition.. but in the wild, the amazon is one huge helluva big river.. again this comes to space and food availability.. do let us know the feed and the feeding pattern for you aros.. do you give them feeders? you could probably chuck in say 20 or 30 small goldfish(post quarantine) and see if it helps.. and pictures of the setup please if you could.. cheers..