Hey Paco,
A few questions regarding your tank and some comments. It sounds like your tank is out of balance. First, you mention RO water, is that all you're using? Are you adding something to get your hardness levels up, because RO water is pure water with nothing in it. Using CO2, you really need to have a kh of 3 or higher. Plants also need Ca, and Mg, again, which RO water has not. What's your gh?
What are your CO2 levels? Just knowing your bubble rate tells you nothing about your CO2 content of your water.
The cyano (blue-green algae) is brought on by low nitrates, which, as has NE said, you have. You need nitrate levels in the 10-20ppm range. Your phosphate levels need to be in the 2-4ppm range. The Redfield Ratio is something a few folks believe works, personally I don't. You need to have all plant nutrients present in a little excess, ratios are not that important.
Check out the following references to help you out.
http://www.aquatic-plants.org/articl...ges/index.html http://www.barrreport.com/forums/showthread.php?t=1 http://www.rexgrigg.com/