Dead spots in flowering! Help?

So this is my first grow, I'm 5 weeks into fowering, growing in coco, and I've slowly noticed my lower fan leaves turning yellow, I wasn't worried because I've heard it's normal during the flowering stage but they are starting to crinkle and die pretty rapidly and now I'm getting worried. Any suggestions?

Had this problem 1st grow was , in my case it was ph problems lack of ph meter.

I actually just noticed I misread my nutrient chart! I haven't been giving them enough of the bloom nutrient mix. Just flushed them with a full dose, pH at 5.8, so I will see how they are tomorrow!

Do you have a TDS meter? If the leaves are getting brittle then you may have a lockout issue. Any time you flush, it's a good idea to flush with clean water, three times the volume of the container. Sorry if this is old news to you. Worth asking since it's your first run. Good luck! And props for getting this far. Those lil' buds are frosting up nicely!

5 weeks in, could be a few things.. low nitrogen or too much p..