Cant see what your seeing pictures are not clear enough. Do see discoloration on head, but doesn't look like velvet. One spot looks like it moved on left side. Could be mucus spots, or sand. If fine spots start popping up most definitely copper treatment. Same with growing amount of larger spots. I think time and better pictures could help in diagnosis. Sometimes time is an option.Are you saying copper the Dt now? Reason being if Achilles have it they all will need treatment fast.
Tarnish brown sheen on forehead and back around dorsal observed.
I have dosed the DT in the past with good success. Tastes a bit to reach therapeutic levels and of course I’ve worked hard to get rid of it from my tank so it stinks I may have to do it again.