I screwed up, Now everything is bad?

Do not give up. Sometimes mistakes in fish keeping are just unavoidable. Many times its hard to tell what went wrong also. So just keep on trying, and maybe just go a few tanks at a time. Are these tanks all running from the same filtration system? If there was an outbreak of some sort, it could very well have spread through all the systems. Mistakes in fish keeping can be costly to your ego and wallet, but don't give up! Good luck.