Clown with Brooklynella

So I am 100% new to this. I have done a lot or research and thought I was going down the right road. I have a 90 gallon tank, live sand,dry rock and I let it complete the cycle for about 2 months. So after that my water had tested good for about a week and I took the kids to get 2 clown fish. After we got home I let the fish get acclimated to my tank and then put them in. One is doing great the other not so much I thought that he was stressed but after a week has gone he is getting worst. After a lot of reading I feel that he had brooklynella I know this is not good. I also think he might have passed it to the other clown I have taken them out and put them in my QT. So here is where my questions start.......

1) LFS said use copper treatment in my QT? YES or NO
2)With both in my QT should I get Formaldehyde and try to treat both in a 1 gallon bucket(I have seen a few people try this)?
3)Do I need to do anything to my DT so when I put them back in I dont have any problems?

I know the one is on the very bad side and has a slim chance but I feel bad and would like to do all I can. Also any chance I messed up or just back luck.

Thanks for the help and I am trying to get pictures just very hard they are still very active.