I agree with the amano shrimp suggestion - I had a diatom bloom just like yours when I set up my 20 gal and the three amanos I put in there cleaned it up within the week! It was awesome.
See if you can get your hands on some more fast growing plants too - maybe some floaters like frogbit/duckweed. They'll also help keep the light levels down a bit.
Lots of other good suggestions here - just don't get discouraged! Lots of new tanks have a rough start. Stick with it and it'll be all the more satisfying when it matures and looks pretty!
Low tech lover and recovering lurker.