Nutrient n deficiency is a lack of a particular nutrient, in this case, nitrogen. I'm not sure what coco A & B is, but if this is hydro, check your food. On the bottles should be how much of each essential nutrient is in it. Use more of the solution with more nitrogen in your next feed. If it's in soil, do the same thing, but with soil based nutrients instead of hydroponic nutrients. Take a look on google, you should be able to find lots of food with nitrogen , or lots of ways to supplement nitrogen using other means.