No - copper power and coppersafe are mild, but they are very slow to work. I've seen active ich infections in treated tanks for 10 to 14 days after the copper had reached a full dose. However, not 30 days like in this case.
Just checking - you aren't seeing any flashing/scratching with the clownfish, right? I just want to rule out flukes.
Since you are confident that the copper treatment is appropriate, then idiopathic mucus plugs would be the next logical conclusion. I've seen that in hepatus tangs during copper treatments, but not clownfish. Still, there isn't much else it could be. No treatment for this other than to reduce the copper levels and wait.
Jay