5 dead cardinals the morning after purchase
So I added 18 cardinals yesterday afternoon to the 4 I bought a week ago and then when I woke up this morning, there were 5 dead ones! This scares me a lot because they looked fine yesterday. I added them to my discus tank so I was worried my discus might catch this killer. The discus are afraid of the cardinals so it wasn't them that committed the massacre. They were purchased from petsmart (not sure if that might be why) after being shipped there as well the same day of purchase. So should I get rid of all of the cardinals for fear of passed infection to my kings of the aquarium, get rid of a few that seem to have white on their face or torn fins (i thought this might be from abusive shipping), or keep the survivors?
Answers much appreciated as I've never kept cardinals before.