Leaves Yellowing for No Good Reason

I am having a little problem with my latest grow, and wanted to seek help for all the grow gurus on roll it up. I am at day 30 of flowering and this is my first grow using the dyna-gro line of nutes and I am having a problem with my water fans yellowing. The buds are looking better than any grow I have done yet. Most the plants are looking great but I am noticing more and more that across the whole grow some my fans are yellowing and dying. it looks like at the end of my grows when I start flushing. I wanted to know if this is from lack of nutes because that is what I am thinking, or what ever else it could be.

My setup:

5x5 area with a 1000 watt hps
3 gallon grow bags with coco perlite mix

nutes I am using ( I water every other day with R/O water):

Dyna-Gro Bloom 1/2 teaspoon/gal every other watering
Dyna-Gro Pro-Tekt 1/2 teaspoon/gal every watering
Botanicare Cal-Mag 1 teaspoon/gal every watering
Humbolts Own Gravity 1 ml/gal every watering
Humbolts Own Snow Storm 1/2 teaspoon/gal every watering




I know some of the fans look black, but its just a shadow because I took these with my camera phone and a mag light



any help from anyone has would great.

Thanks

i guess never mind, my buddy said it is a lack potassium. Just going to use some meta k by earth juice to correct the problem

potassium is for sugar production. phosphorus and iron is for leaf and flower growth during bloom stage. up your bloom nutes.

possibly magnesium def.... Can you get a pic of the whole plant?