Columbian Red Fin With Black Marks And Possible Eye Issues

I have 5 Columbian Red Fins .They're 3 years old. Recently I've noticed they've all developed black marks on their bodies. In addition 2 of them seem to have eye issues. They're like white spots/marks(no sign of white spot problems) actually on their eyes. They all look and act well.
I did have barbs and their number went down gradually to three(they've now gone back to the shop) but i didn't see any signs of them attacking the red fins -or my other fish.
Can anyone help please?
Many thanks Ros

I've just found a very similar thread on another forum (unless you go by the user name mrvillicus elsewhere?). Someone with columbian red fin tetras which have developed black spots. I will be keeping an eye on that thread......

Hello Sue and anyone else who may interested in the Red Fins
On Sunday I was unexpectedly able to get to my not so local fish place. They believe the marks are  likely to have been caused by stress - too few barbs not having enough of their own to be agressive with- This would cause both  a loss of pigmentation, and  a mucus over the eye. Interestingly it is the largest of the Red Fins with the most marks.
Anyway, they recommended Melafix, to cover bacterial possibilites and  which they say  is herbal( i  remember reading the same thing  on the old forum and it appeared to be generally well thought of)They also sayit  helps to perk them up and the instructions say its  useful when introducing new fish - which i did Sunday,  my first ever guppies and beautiful they are too.
Ros

Thanks Sue