Nitrogen deficiency???

Is this a nitrogen deficiency? I'm 7 weeks into flowering, and have been using mostly 15-30-15, but have hit it twice with 12-55-6 super bloom. The newer growth is dark green, but the bigger older fan leaves are turning yellow. I understand the plant designates most of it's power to bud growth, but these leaves look like they are about to fall off.

That's pretty typical of plants this far along in flowering. Doesn't look like anything to worry about.