Hey,
hope the prazi treatment is working. It was the right thing to do.
It is important to keep rays and other fish in a stable environment, only add new fish after weeks of quarantaine and treatment. This is were it often goes wrong.... too much enthousiasm too many fish too fast etc.. etc..
If there is chlorine in the water use a showerhead to to waterchanges, most of the chlorine will evaporate while spraying the fresh water into the tank.
Greetings Mark