Are you QT'ing or just throwing them all in the DT? Are they big/small? Are they all from the same supplier? Be more specific when you say "sick." Are they scratching, red marks on the body, stop eating and die of starvation, suddenly die, etc? How many fish in the tank?
timdam;18962289- sick as in scratching said:That would indicate flukes and should be treated for (as stated above) and this means you have flukes in your system and unless you treat the whole tank all new angels (and other fish) will get it. The severity will depend on the health of the fish, but since all newly caught fish are pretty stressed their defenses will be down. Angels are notorious for comming in with flukes.
I don't introduce a single fish into any of my aquariums unless they have been treated for flukes.