Velvet

So 3 weeks ago my tank got a velvet outbreak I immediately removed every single fish from the tank and put them in qt and have been treating them with .4mg of cuparmine so far i have only lost 3 fish but I have a few questions
I have a golden dwarf moray eel that i know doesn't have velvet i know they are pretty resistant to the parasite but really sensitive to copper do you guys think il be okay putting the eel back into my display tank?
How long should i keep treating the rest of my fish? they are all clear of velvet eating amazingly well, very active, they all seem like normal healthy fish I'm just concerned about them getting it again once they go back into my display tank