Quarantining

[spicyburrito]

Hi,

I currently have a few fish in quarantine after my Powder Brown developed a few white spots.

I've had the fish in a 60L tank for a bit over 3 1/2 weeks now using cupramine but I am worried about leaving the fish in such a small tank for the remainder of time the dt needs to be kept fallow.

I also have an aquamarine 900 which i have setup to transfer the fish out of the small qt but all the 120l litres in this other tank is brand new saltwater.
as the tank hasn't had time to cycle would I be able to combat this through doing frequent larger water changes?

I dont want to get more water out of the dt as it will put me back to the start in the timeframe to ensure that the fish are ich free

any advice would be appreciated