I've been a gardener for 50 years and learned early on if something dies after I've given it my best efforts, not to get sentimental. Dig those suckers and sickies out and plant more of what grows well. I approach my fish hobby the same. If a species doesn't do well with my conditions and efforts, find species that will thrive under my best efforts and collect those. I don't enjoy set backs but I do learn from them.