What is this stuff growing in my fish tank???

i cleaned my fish tank, and after i started getting this green moss stuff in it..at least i think it is like moss....it is definately not a dirty tank (25gal cleaned every week and only 4 fish), and not on the gl...it is just growing off everything in the tank, even the gravel....it is thin, green, and is like little tufts of hair in my tank..........anyone?