Black specs on the glass sounds a bit like Danio fry, but they are incredibly small. If the fry are a bit larger, it's probably one of the Livebearers. Any chance of a picture?
I am almost positive that they are danio fry! They are born looking like eyelashes, and cling to the sides of the glass for the most part.. some eggs are buried in the gravel and escape hungry mouths, but dont be too excited, they wont last long.. they usually need certain types of food and are easily eaten as they dont swim away very fast when a fish approaches.. I watched my platies gobble up my danio fry.