I just got myself a silver arowana same time as u, and same size as yours, and it has not taken a liking to the freeze dried plankton that the LFS sold to me. However it does love the mini hikari pellets i drop in there. I think its getting bigger already. Did u say u were giving urs krill?
He was fine for the last few weeks. He was eating well, the water was always good with ammonia, nitrites, nitrates, etc. He just stopped eating yesterday and now he's dying. What went wrong?