I have tried to read through the thread but pardon me if I missed something. What type of filter and filter media are you using? What chemicals, if any, besides Prime are you using? There are several different types of filters and media that say they remove ammonia, nitrite and nitrate. If you are using those, that would explain why they are all zero. It would also mean that the tank may indeed not be cycled even after a year. It still wouldn't explain all the deaths though. Those filters would, however, most likely remove any medication that you might be using.