Just saw your video Victor, i am so sorry for the loss of the RTC and the TSN. I suggest creating a separate, large quarantine tank/pond, one with sufficient dimensions. The fish you rescued in this video seemed stressed due to the reasons you mentioned, but also due to the shallow water in the tank and the treatment part was the final blow. In my opinion, you should have placed the fish in a proper quarantine pond/tank, wait for a day or two for their stress to reduce, and then begin the treatment.
You can also use kiddie pools as quarantine ponds if buying additional tanks isn't possible or hard for you.
Just my two cents