Acclimating the fish could be the issue, if I had to think of something I could be more diligent with. I typically drip for 45 minutes. But I know for some of the fish over the past year I have spent less time than this. But even with the fish that I dripped between 45 minutes to an hour, they all eventually died, too. I get all my fish from the same 2 stores: a Petco, and a 'high-end' saltwater fish shop. I have noticed no advantages to buying from either place.