I have 0 nitrate with 4 bta's and they are fine (that is just me, everyone is different). I do dose amino acids everyday though. I wouldn't mess with your lights too much. Stability is key, but it is hard finding that balance. How many lights do you have? Just LED's? Any t5's? One other thing I have learned is if the water was polluted by something (aerosol, paint fumes, drywall dust etc.) that could have a negative effect on the nems. My bta's like clean water and intense light.