Most of the LFS have all their tanks on one system so all the fish water gets redistributed to all the tanks. Stress of acclimation, transport, etc. only weakens their immune systems. I looked up a link to help you for your next additions and I read it and also learned a few things (you never know what you don't know!)! Since you have an idea as to what your fish had, I might research the bacteria and see if it is something that can lay dormant in your system or if it is gone once it no longer has a host. I know ich has a dormant stage but can't remember how long. I'm so happy you are sticking with it!