I did not properly clean out the trash can prior to doing the change. That was dumb of me. However the 43 never had any issues and I not only used the same can but the same water from it.
Prior to the change my parameters were good except for the salinity waslingering around 30. That was the original reason for the change. However I go back to the tome frame. Everything died within a few hours of each other two days later.
If I said zero nitrates I misspoke. They are just nearly undetectible. 5 at highest. I have not had issues with them in the past.
I'm am on day three after the fish tank armeggedan now. The eel's breathing is completely normal now. I still think it was an issue with o2. That is the only thing I have changed scince it happened. The eel went from unable to move to completely normal in three days. I'm gonna keep things going the way they are now for a few weeks then start restocking.