with aros its best to have odd number in the same tank. you should put some floating plants. my friend had 2 silvers, one was swimming around(dominant), and the other was the corner guy(weaker). so he gave the weaker one to me. he was beat up bad. now he is fully recovered and living with my jardini. it really hard to say. do you have any other tank mates beside the four silvers? a pic would help. and what size are the silvers
I woulda thought that 4 was enough to form a shoal. My two silver aros swim in unison backward and forward with asian one on the fringe (although one gets to eat first all the time, the other musta accepted the dominance). The other tank also sees 2 paimas swimming together all the time (with jar and silver by themselves and not in the corner) - same here, biggest paima eats first.
Did you get your aros from the same place? If so, that is even more weird, cos LFSwoulda been kept them together. I would try to separate the tank in half (assuming your aros are not yet too big) and keep on dominant on one side and the other three on the other. See if the three can get along or not. If they do, feed them for awhile and combine after some days. If problem persist, separate the loner. If not, will try to think of something else.
no need to sperate the aggressive one, all you need is more fish. add a few parrot fish or sevendum in there to act as dither fish. and reduce the lighting if you have strong light.