ok problem solved
my silver arowana just doesnt like competing for food,as a surface dweller obviously he is king of the tank,so when i put the 2 archers in (well) the archers were invading his territory as the archers are surface dwellers too,both archers & arowana were competing for food at first..

they have settled although my silver arowana wont allow archers to the surface,,i think in time they will adjust.
when aro is full he will move away & allow archers to feed.

cheers
chris!!