I have several fishes when newly bought have few or no black specks. They include Super melon, Golden melon, Yellow crystal and golden. I was told that they have pigeon blood ancestors and will have minimal black specks. Nevertheless, even after treatment using PP bath, the black specks remains.
The fishes are eating and swimming with no other signs of sickness. I’m doing metron pills de-worming soon but doubt it will improve on the specks.
When the genes have black peppering (or specks), it will show accordingly. We cannot use any medication or treatment to remove the peppering.
If you the peppering you see temporary, ie sometimes it shows and at times it disappear, it is caused by stress. Put an overhead light, so they are not able to see movements outside the tank, choose a quiet area so they are not startled by vibrations.
Now there are many improved breeds you mentioned without black specks or peppering even when stressed ie our Checkerboard Pigeon has no black peppering.