Will help what? I mean - Metronidazole can help certain diseases, melafix is supposed to help certain diseases (though there is a fair bit of debate here). Copper of course is used against various protozoans. It is a good idea to have a diagnosis (or at least a really good idea at one) - IME, before mixing drugs and treatments. - and the treatments themselves can be toxic. In other words - it would be fine to fallow your tank by putting your clowns in copper - again I would not personally add metronidazole. It would be nice to see the fungal infection on the tang (copper does not treat this, per se, neither does metronidazole - nor do either help with HLLE). I don't know why copper + Melafix would be ok for the tang, but not the clowns?
The problem is - let's say your clowns are carrying a parasite - but are not showing symptoms. Once you place new fish in the display tank, you may have an outbreak - which is why after an issue like this its sometimes better to start over and QT all of your fish and leave your tank fallow. Note - If this represents Uronema - I do not believe you will be able to 'cure it' with medications.