Quarantine Tank Help

[daplatapus]

Congrats on the upgrade.
My first question would be how often did you do water changes? Is there any type of filtration on the QT? One of the big killers in a QT will be your Ammonia. The more fish in the QT the faster your ammonia will climb. Having a filter system that's got the bacteria you need to process that ammonia is the key. Or using something like Amquel to treat it.