Jardinis have been known to be one of the nastiest arows the world has to offer....if u scour the threads...u can find that they do alot of damage....two of them together...is like sabotaging a nuclear reactor.
So obviously the aros were put in the tank when they were alreasy monsters. But what if they were put in a tank at the same time when there still babys?
From what I've read, once Jar's hit about 11 inches they tend to go psychotic and attack/eat/kill the other tank mates.
I'm not speaking from experiance here.