I agree - I have fish die in quarantine but they don’t die FROM quarantine. That is to say, the methods I employ don’t kill the fish, but the method doesn’t solve every issue - some, like microsporidians, can’t be treated. I’d rather have those fish die in quarantine than carry that scourge into my displays.Fish dying in QT is likely because they were introduced to the medicines too late, at too low of a level, or the keeper failed to manage some other aspect (stress, oxygen, ammonia, etc.). Your lfs likely tells you that qt kills because they are wanting to sell you fish and not have you wait 45 days between every purchase. LFS are not a good source of unbiased information. They are salesmen and people foolishly take their advice as honest information. If an LFS were to give people proper advice, their sales would drop across all of their livestock.
Jay