Honestly that tank is quite small for arowana long term, it would maybe juuuust barely do for an adult jardini. But in a tank which is minimum for a very aggressive fish, tankmates are going to be very tough to pull off. There are plenty of other cool fish which would work with Oscars in a 180, such as flagtail prochilodus, pinktail chalceus, to name a couple. I will move this thread to the arowana subforum where more arowana keepers will hopefully respond. But I think if you want to try a Jar in a 180, it's going to have to be alone, and if you want a community of fish, an arowana isn't going to be the right fish for you, in this size tank.