That doesn't sound like ich/ick to me.
ich/ick is characterised by small white spots see pic.
Any chance of you posting a pic? It could just be that the fish has injured himself on something sharp in your aquarium, but without seeing a pic it's almost impossible to tell for sure.
Size of tank in gallons or litres.
How many fish and which type.
Water stats in ammonia, nitrite, nitrate, and ph.
Does the fish show any of these signs.
Flicking and rubbing, excess mucas, erratic swimming, darting, laboured breathing or gasping.
The mark is it beneath the skin or on top.
Does it look like bleaching of the skin.
is it possible to load a pic up.
Could the fish have scraped itself on something in the tank, or a heater burn.
Ok.
Just add some myxazin by waterlife to the tank if there showing no signs of parasites.
Myxazin would be better.
Some fish don't tolerate melafix towell, so if you do add it only half dose.
It dosn't sound like a parasite, it could be columnaris, scrape.
Any signs of the scales been lifted up.
Columnaris has many diguises.
It can show itself in so many ways.