You don't need to lower salinity if you're already dosing with copper. In my experience, Seachem's Cupramine is the safest copper treatment on the market. Keep the concentration at 0.5mg/liter. Although the bottle says that most fish tolerate it up to 0.8mg/liter, I really try not to overdose. Although copper has been reported to be effective against flukes, I've found prazi-pro (praziquantel) to be more effective. I dose Cupramine and Prazi-Pro concurrently all the time and it's perfectly safe.