Looks Like Blood On The Tail Of My Fish

[debiasir]

on the tail of my fancy goldfish there is an area that is roughly 5mm circle of what appears to be blood but it also looks like it is flaking off. it is not actually bleeding if you get me but looks like it must have been. its not bright red either. only came today as i observe him daily. He is swimming, eating and pooping as normal and doesnt seem effected. I dont have access to meds. I think maybe he caught it on the screwcumber as i left that in overnight.

anything i can do or does it seem ok.

 

[WILDER]

How many gallons or litres is the tank.
How many fish and which type.
Water stats in ammonia,nitrite,nitrate,and ph.
So it red but is looks like it flaking off.
Or does it look like a fine red gold dust.