I agree with mnfish1 that the most likely problem given the information you've given is an already unhealthy fish. Generally you should feel pretty good about your qt setup and its thoughtfulness. Don't let the losses get you down too much. It sucks that it happens, but it's clear you care and are trying hard, so keep it up!I'll try going the mesh route. I can say though... Fish have made it through a full QT protocol in this tank on multiple occasions. In May when I got hit with velvet I had about 5 fish make it through. In September when ich struck I had probably 12 fish go through it with no issues.