its hair algea, it'll quickly take over your tank, my 15 g has been infested, its under control now. No fish will eat it, so don't try that. Ive tried pl*co's, Ottocinclus, algea eaters, etc.
Best way to get rid of it is to scrap off what you have now and removed it from the tank, and do more frequient water changes, less light and less feeding.
if your really desperate and want to use chemicals, i'd recommend Green-X-.