I lost both of mine afew months back shortly after I started feeding them silverside, my other fish might of been stressing them out as well since I had a few fin nippers. But I think they have a problem with the frozen silverside tho, I've seen other posts on here about the same thing. All my other fish were fine so the tank was ok, if it was something in the water my ray would of started acting up, the only other fish that was acting funny was my AGTF but I was giving him silver side too. After my last armatus went I stopped using silver side and the tigers back to normal and doing better. I'll be getting another armatus in the summer but I'm going to stay away from silverside tho to see if I have any problems. But he was almost a foot when I lost him. It was one of the hardest losses I have been through, but then agen I haven't lost a fish besides the armatus in over5 years.