Hey! If you haven't been feeding your plants, it's a deficiency. Otherwise, it could be a nutrient lockout due to a very high EC. I recommend measuring the pH and EC of the runoff water; if the parameters are optimal, you should start/increase your nutrient doses.
I see magnesium, and slight potassium deficiency. Check your substrate ph as well. Might be shifting out of range, if not it just need more nutrients in those areas. Good luck 🌱