Clownfish problem

[jtbadco]

Looks more like Brooklynela or Velvet to me from the pics. If it's Brook then you will see pieces of skin start to fall off and the Copper will not help. Formalin would work but it may be too late by the looks of the fish.
If its velvet then the Copper should do the trick, but you will need to remove and treat all of the livestock and leave the DT empty of fish for the treatment period.