I put 10" Koi into Arm's tank. Nothing happened. YET.
I'll wait for 3-4 days to make sure. My Arm always has bad attitude against slow object like goldfish, my hand, but not things that dart around him. He never eat or attack fast object like Comet or Koi before. I wish I could have some luck with the combination IF my Koi do survive. Yes, IF.