i had a deal similiar to what you are going through, and of course it was all error on my part during the last transplant to bigger pots.
Instead of moistening the soil b4 i transplanted, i ended up using the mix dry, putting the plants in the soil, then completley drowned em with water..... haha my bad cuz my plants really started turning yellow, and of course i mistook this for low nitrogen. so i watered them some more with some fox farms grow big, and big bloom. My problem got worse, and the reason for this is that i am drowning my poor plants, the roots cannot get the air they need.
So what i did that completley cured my problem.
I removed my plants from the super wet soil, grabbed the bag of new dry soil, and re-transplanted them, i took the wet soil out, removed half the contents into a bag, and mixed in dry soil with the half of container of wet soil... mixed well it was nice and moist... just perfect for my plants. Then i just gave them a blast of big bloom in a foliar spray.
this seemed to snap my plants right out of their pale and yellow look, new shoots are nice and green, with green not purple or red stems.
i dont know if this will help you at all, but i figured since it workded for me, id spread the love here, and hopefully help a few others.
for sure one of the biggest mistakes newer people make is overwatering.
these plants were around 24 inches when they started turning yellow. I was planning on putting them into flower on xmas, but thats the day i noticed things going pale, so needless to say that didnt happen. I for sure want to go into flower with healthy plants not sickly ones.
I love this flippin site!!!!
~BBA