YELLOWING DURING FLOWERING?

At the top you put 5 ml cal-mag, is that every feeding? If so the back of my head says overdose, especially since a lot of plant don't like heavy cal-mag in flower. @Mr. Grow It , calcium being immobile would affect the top first being youngest right? And could also lock out other nutrients I believe. Definitely got me a little stumped.

Is the 6.5 PH , 1500 PPM you mention the runoff measurements?

And the fox farm nutrients usually covers that but I would just go to higher dose , not exceeding the FF recommended amount for now.

Mine are usually around that size at that time, some strains bigger. Bud development starts what seems slow then just starts plumping up, most growth in last couple weeks of flower. I'm pretty sure you'll probably have a lower ppm on the run off and need to increase nutrient amount. 4 weeks in flower at half dose usually isnt enough.

I could be wrong but it looks like zinc deficiency. Cold you get a run off pH and ppm?