My chalceus recently passed. I got him when he was 3" and he was about 10-11" when he died. My initial research told me they were semi aggressive and would pick off little fish. This was not my experience. He was very placid and never bothered any of my other fish. He was in a 180g glass tank for the most part but as he grew he started to get more skittish. Sudden movement would occasionally freak him out. Eventually I put him in my fibreglass 360g and the skittishness stopped immediately, he went back to being proper chilled again.
They dwell in the top level of the tank, same as arowanas unfortunately, sometimes just staying motionless for long periods of time, waiting for that sudden plop of food, and then BAM! they spring into life. Mine used to love garden worms but would eat pellets, flake, loved prawns too. But never ever did I offer him live.
They like a current too, I achieved this with powerheads which came on intermittently. He liked to swim in the strong current for seconds at a time, almost as if he was testing his own strength.
All in all a brilliant fish but as mentioned in other posts a chalceus in your tank may be out of their depth and get picked on, or eaten, especially patrolling the same top level of water as your aro.
Honestly, i'd pass.
