Keep an eye on them. In a tank that size, they may just do a chase or spar up for a few seconds and move on for a couple minutes. It may still be enough to cause some damage and have one of the aros without an appetite sooner or later. You will have to get a sense yourself if it's time to separate if needed. But generally, when 2 aros start fighting..it doesn't stop. Adding tankmates could distract them and maybe even stop things, but not the norm. Tankmates would have to be small and not a threat to eat them of course. You could add more aros (to disperse aggression), but i don't recommend it unless a REAL big tank is planned. It's all a crapshoot though. IMO, one aro is best for long term keep if you want to avoid possible headaches down the line. But you never know with individual aro personalities. They just may get along great for life. You will have to upgrade for long term keep of 1 or 2 of them as you may already know