Hi
If the new growth of a plant contains yellowing, it is probably suffering from Sulfur deficiency. This deficiency can be cured by mixing one tablespoon of Epsom salts per gallon of water until the plant's condition improves. If the yellowing is the old growth on the plant this is normal coming into flower and nothing to worry about.
If you want bigger buds, a good part of advanced nutrients is 'big bud' have a look, it really does fatten up your buds and give you some extra size. By the end of your flower stretch which last around 3 weeks, you want to completely cut out Nitrogen and only be using P and K. Using too much N after the stretch point will just slow down your bud growth.
+1 strain
