flowerhorn can live with no species (I think)
because when they mature they kill any fish they can (my experience)
even the pleco which grow with it is killed after the fh mature.
So if you want to keep it, please consider to keep it alone in a tank.
That is the common way we do in hong kong
for the silver arowana, if it is kept for long term, maybe a 1.2M/ 4 feet long tank is needed. it is quite gentle when compare to other arowana such as red tail gold. I love this species
yeah i was just about to say that degado has done it, and not just with his arow but with other fish to. but if they wont get along i would sell the arow, as you need a big *** tank for him in the near future