I keep my nitrates around 10ppm (API test kit). When it reads 20 I usually do a 10% water change and that usually gets me back down to 10. My phosphates I keep between 0.00 and 0.03 (Hanna). Once they start going above 0.03 I know its time to change my media. I haven't had any cyano issues and I feed a lot with frequent AA and trace element dosing. If your having problems with cyano I would take a look at your phosphates first. Lower them down slowly, feed less, and wait until it dies out. Then slowly ramp up your feeding until you find a happy medium.