Armatus grow very quickly when the proper conditions are present....but like most characins, even predatory characins...they are very finnicky and easily startled. Think young Piranha, Atf's, etc...mine came in with a damged nose, and took a month or so to heal...every time he was startled he would charge the glass and re-injure it. I kept the tank 3/4 covered with black garbage bags to keep him settled. He has now grown out of it, and if feels unsure simply goes to an area with cover...but is much more curious and up front now. If keeping it with other fish I suggest bottom dwellers, and fish that do not startle easy....I have mine with some clown loaches, catfish and a couple of baby cichla....he ignores everyone....but is definitely territorial. from what I have observed, they get very active in the evening, and that is when mine atleast does the majority of his hunting....just make sure to always keep the tank stocked with feeders and he'll grow before your eyes. Also, I suggest upping the filtration so you could cut back on the water changes...the less stress you put him through....the better.
