please HELP, 2 plants, 1 healthy as hell and the other... ehhh

my grapefruit diesel is doing amazing in week 5 of flower, nice and green

but my purp diesel is yellowing and developing more brown spots by the day!! all leaves are dying and now im getting worried..

both in soil, fed every other week with half the dose of ff nutes..

i stopped feeding the purp diesel, but should i flush? (the pot is heavy as hell, almost like it didnt drink any water)

or should i repot do avoid root rot??

im not sure what to do but would like some advice..

and my grapefruit diesel is at least 1/3 bigger and the buds are at least double the size of the bud son the purp.. week 5 of flower on an 7 1/2 week strain, please HELP

do as little as possible for them

they are like nomadic children give them too much love they will hate you forever and run away give them freedom they will keep coming back for money.

lol that was good, well that leads me to my next question.. should i flush? or will i do more damage and drowned the roots?

like i said, the pot is heavy still and i watered 4 days ago.. should i just let it dry? i dont want it to stress out, hermie on me and pollinate my beautifulllll GFD. any more advice is greatly appreciated..