Judging by the fins it could have had a bacterial infection which Cb could have taken out both of your clients if they were fighting. Clowns are very susceptible to marine velvet and flukes which are very common as well. If your buying clowns from a local store, and they are housed with any other fish at all, I would do a minimum of 2 doses of prazi pro 5 days apart no matter what. At least would rule out the most common parasite and you can even do that in your display. I would always recommend quarantine though. Even for you nano guys...