These may be hyper-melanization which gives a fish this appearance after being stung by an anemone or coral such euphyllia. Do you have either in the tank?
If so, provide good water quality and diet and will heal on it own and not a disease.
If not, other would be black ich , and not Ich, the disease. They would be turbellarian worms and likely the Paravortex version which are smaller and appear as grains of black spots
These worms have a single host life cycle producing several juveniles which can last up to 30 days but rarely do. Best is to treat with Praziquantel better known as prazi pro for two 8 day intervals with a water change on day 9.
other option is formalin based medication such as quick cure or ruby Rally Pro starting with a bath for 45 minutes followed by treatment
Do note that Prazi will lower both oxygen and appetite, so an airstone is recommended for added aeration and monitor water quality during treatment with a reliable test kit
