Fish Frank, Acara are very closely related to green terrors. It's been my experience with the GT's that keeping two males in a tank is very difficult. Chances are your acara are males. Thankfully Acaras are a much more docile fish than their GT cousins. My daughter kept a single 5" electric blue Acara in a community tank with no aggression problems. It's likely things will work once they establish boundaries. Nice tank.