Yellow leaves near the harvest

I would say your problems are more down to over feeding and growing at 24/0. All cannabis plants NEED sleep to finish their photosynthesis cycle and to have a correctly functioning metabolism. 18/6 is optimum, but it is never too late to switch to this and this may just increase the quality of your final harvest. The MYTH that it is ok to grow cannbis for weeks/months without sleep needs to be removed from history asap! A lot of metabolic processes occur during the night, so without sleep, these thing do not happen, leading to plants with messed up metabolisms - and a plant with a messed up metabolism will never produce the best quality it is capable of. For a newbie I suggest waiting until there are about 95-97% brown pistils, start your "flush" (stop all fertilizers actually) and harvest about two weeks later when there are about 98-99% brown pistils. This will give you buds with peak THC levels and moderate CBD levels, producing a well developed and well balanced high. This will also correspond to the oft quoted "10-30% amber trichomes" zone, without having to look too closely and is also very easy to understand.