Whats Wrong With My Fish? Illness

[Soundspeedy]

Hello all,
Recently my colombian tetras started getting black marks on them, I had no idea what it was but thought nothing of it. Now one has small 'pimples' on it. I dont think its whitespot as the pimples are larger and only affecting where these marks were. My other columbian tetra has got these marks but not the pimples. I have also now seen one of these pimples on my Gold Severum.
Any ideas what it is or has anyone else experianced it? How do i treat it?
Danny

 

[KISSfn]

Try posting in the Emergency section.