Howdy,
Blue-green algae (cyano bacteria) are tough to get rid of
. The only remedy that I have successfully used against them was Redoxin from Aqua Technic. That's sold in Germany, but you may be able to get it off e-bay.
Besides that, I recommend frequent, big water changes (5-7x/week) during which you thoroughly remove any blue-green algae you can spot.
Good luck,
HarleyK