If yellowing begins at the oldest foliage and progresses upward, it is a nitrogen deficiency. If it starts at the top of the plant it could be calcium deficiency. Here's a blog that you may find helpful to navigate the issue: https://futureharvest.com/blogs/articles/how-to-identify-cannabis-nutrient-deficiencies?_pos=1&_sid=aa883d910&_ss=r
From the pictures it looks like you may be low on the nitrogen, in which case, adding more of your bloom cycle fertilizer would be recommended. Future Harvest's Calnesium is also a great way to prevent calcium and magnesium deficiencies while increasing nitrogen. Hope this helps! -Bryce from Future Harvest Nutrients