I have added Panacur to prey items also; while I'm comfortable with tube-feeding/medicating snakes, the need for daily tubing would get "old" for the
snake so putting the medication into prey taken voluntarily would be best. (normally tube-FEEDING is never done daily or anywhere near that often)

That's unfortunate that the black snake died but I seriously doubt that was because of anything you did. I don't routinely treat snakes with Panacur unless
I have reason to suspect it's needed (seeing poor condition, weight loss, poor appetite, regurgitation, funky stools including diarrhea); in this case, knowing
it has coccidia, I'd probably want to treat it.