The link in my signature is a treasure trove of info with links to the "fish in" and other articles as well.
So sorry to hear of the losses. I had had tanks for 30 years and found out that there were important things I didn't yet know! One of the most critical was about the nitrogen cycle and BB (beneficial bacteria). As an aside, rinsing the filter pads in untreated tap water kills the bb, and throwing away the filter pads every month throws away your bb. Hope you find some good useful info in the articles.