I'm not certain that copper does it - I would venture to believe that when folks experience HLLE in a copper treated QT - it's because of poor water quality. I've QT'd over 30 fish with copper, and only had HLLE start on 2 fish, interestingly enough in a Qtank that wasn't cycled properly and had excess ammonia - upon moving those fish to another QT tank (copper treated) with a proper filter, it cleared right up.
HLLE will clear up on it's own, but you need to maintain pristine water and a proper diet of vitamin and amino acid enriched food. Nori should be provided daily as it's nutritional value far surpasses most other frozen or flake food.