Black dots on cardinal fins

[Martin in Holland]

Last evening I spotted one of my cardinal tetras with some black dots on its fins and tail, they are not on the fins but look more like a discoloration of the fins...still tiny though. He/she seems healthy so far and no spots on its body.
Does anyone have an idea what it could be?...should I get worried?...

 

[nickmcmechan]

Not sure if this helps, haven't experienced it before myself

http://www.fishdeals.com/fish_diseases/black_spot/

 

[Martin in Holland]

thank you Nick...but the spots are very different...I googled already alot