Random death of 2 out of 3 aro

I had 3 aros in a 240gal tank. A silver about 11" a black/blue 8" and a 11" jardini. In the tank is also a soft shell turtle a albino tiger Oscar and a catfish. The jardini I believe died from a amoina spike due to fin being burnt it died 3 days ago. And also my blue aro died yesterday randomly at night when I got home before I left he ate his frozen bloodworms and swam in his corner as usual all day and when I came home he was dead so idontknow what cause it. My silver is very healthy swims the whole tank and eats aggressively. There was more fishes in the tank when all 3 was introduce into the tank and I watch them everyday for hours and seems to get along well.