It does sound a bit like Black Ich, "Black Spot Disease appears on the fins and body of fish as tiny black dots, less than the size of a pinhead". It is caused by a parasitic worm of the genus Paravortex. According to the article "Black Spot Disease" (see attached link) it has a similar life cycle as Cryptocaryon irritans (saltwater ich) and the treatments are similar as well.
http://saltaquarium.about.com/cs/com...a/aa041701.htm