I lost 90% of my fish pre QT. I have only lost 2 out of 13 since QTing. I don't know why I lost the first one, think it was a heart attack. I stuck my hand in the tank with a hose to do a WC to lower the salinity for hypo and my mimic I just bought flopped over dead, not breathing. I tried to resuscitate it but I couldn't. The other one died in QT from getting picked on by my purple tang I think. Without QT and hypo I would have lost at least 6 more fish, they were on deaths door until I started hypo.