Yellow Leaves 5th week flower/ First time grower... Help!!!!!!!!!!

Im in my 5th week flower and noticing that my hindu kushs are starting to get a lot of yellow leaves. Is this normal in the end of a plants life? i put a pic of the leaves, they turn yellow and die out. it is mostly at the bottum, is this a lack of light at the bottom? i have 4 plants under each 600w light. Growing in soil useing metro mix. Running advanced nutes- Big bud, kushie kush, b-52, bud candy. With General Hydro for N-P-K and humbo county bud hardner, and adding epso salt for Mg.. PPM at 1150-1250 feeding 3-4 times a week ph 6.25-6.33range. Doing og kush and hindu kush but its mainly showing on the hindu. And some plants have ridges on the side of the leaf and seem to curl up is this Mg Def? Are these normal things? this is my first grow besides this problem my babies are looking good and budding very well

perfectly normal

yea the big fan leaves start to trn yellow from bottom of plant all the way to the top. A decent way of telling when its done. Dont pluck them let the rest of the plant suck all the nutrents out of the leaves.