Rolo's right, your phosphates were too low for your nitrate level.
We all tend to run our levels differently. I usually have 20ppm of nitrate, and keep my phosphate at 1.0ppm. I get a little bit of green spot algae, but even that's going away after changing my source of trace fertilizer.
My suggestion, keep phosphates between .5 and 1.0ppm and nitrates between 5 and 15ppm proportionately, and you shouldn't have the algae issues. Play around with the levels, but keep them stable for 2-3 weeks at a time before deciding whether the level is good or not. It takes several days for a change in your routine to affect the plants.