PHOSPHORUS OR NITROGEN?

NEED SOME HELP I HAVE A NYC DIESEL GROWING IN COCO BUT RECENTLY THE STEMS STARTED TO TURN SOMEWHAT REDDISH.. AS WELL AS MY OTHER PLANTS ( CHERRY BOMB & CATARACT KUSH
 
A few weeks back I was getting a yellow leaf and dying always on the bottom as well recently I haven't but I'm starting to get one on my other small ones
 
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