I also used urea. Moreover, i dosed 3 forms at the same time (NO3, CO(NH2)2 and NH4). I also noticed bigger leaves grow on some plants. The point is (but i'm not 100% sure yet) that by dosing urea and NH4 one can keep lower NO3 levels but maintaining the same growth which is achieved by dosing only NO3 but in higher levels. I didn't notice issues with any type of algae. I was encouraged by "Drak" firm which produces N fertilizer for planted tank which includes 3 forms of nitrogen. The daily dose is 1 ppm NO3, 0.1 ppm NH4 and 0.33 ppm urea.