In the 1990s or around that time there was an angelfish disease that killed lots of angelfish and caused angelfish prices to skyrocket. It has disappeared as far as I know, but maybe it is still around. It killed angelfish one after another and there was not much you could do. I do not know what changed so most angelfish now survive. But you never hear of that angelfish disease anymore.
A more likely cause for what you are seeing is velvet disease. Velvet is somewhat like ich but very much smaller and, when bad, coats the whole body of any fish that gets it. I believe that when it completely covers the fish's body there is not much hope. The infection is real hard to see but in the right light appears to be a light cloudy film over the fish's body.
For killiefish which are really susceptible adding salt and raising the temperature works, particularly as a preventative.
Since you are already at 82, that should be high enough, but adding salt could help, one teaspoon per gallon per day for 3 days maximum.
A dip of the fish in salt water used in a marine tank can rid the fish of the velvet organisms immediately. But do not put them back in the tank that came from since that tank is infected. Put them in a quarantine tank with melafix and/or pimafix to help prevent infections in the wounds that the velvet left.
Look up fish velvet disease on the internet. It will give you lots of details.
