Dinafem Amnesia XXL Auto

I am noticing some slight yellowing in the leaves above the Cotyledons. I believe this might be due to under-feeding (N-deficiency). The 350ppm (0.7EC) is based on tap water (175 ppm), so only about half of the PPM given is the actual nutrient solution. I do see some slight fluctuations in the PPMs day-to-day, but usually no more than 15-30ppm (~5-10%) in either direction, and not predictably so (swings can go in either direction, but not dropping below 340). Roots are bright white, but have only just started being submerged in the solution. Her sister (Dinafem Sour Diesel Auto) does show some root discoloration, but only on the area of the roots that is actually submerged in the solution.