urea

just ordered synthetic urea nitrogen and decide using it in coco it's only nitrogen source i'm going to use for grow plus some pk , will urea work fine in coco ? I know hesi tnt has 100 urea nitrogen in it and is recommended for coco by company , will urea provide nitrogen in coco as well as soil ?

Plant is 6 days old.From today bloody skunk sprout out but one of her cotyledons is yellow with a little bit of a cask on the top i think its beacouse of overwatering or missing the N element from the soil i cant add pictures sorry about that but, my question is do i have to worry , beacouse...