How would you know that, you've only had it for 2 weeks. More likely it had settled in and started eating, with the oscars having nothing to do with it. You can do as you like, there are many who have raised them together with no issues. Then there are those who have lost aro in such set ups. So it is whether or not you are willing to take the risk. I'm sure if you loose the aro, you can always buy another at the LFS.but his appetite went back when i introduce the oscars.
With silver aros it's best to go sooner. Not sure if you realize how fast silvers grow. Yours looks to be 5-6" long, within 6 months it will be 12-15" long. In as short as one years time you'll have a monster on your hands that will be in the 20-24" range.Ill try to get a tank sooner or later.