The leaves toward the bottom are important, they are the first to be used up if the plant lacks any essential elements. Discolouration at the top of the plants is due to over fertilizing or other factor. Its best to monitor the bottom leaves carefully because they will tell you first what your plant is lacking. It would probaly be best to go for something in equal parts like 20-20-20 with trace elements Boron,Copper,Iron,Manganese,Molybdem,Zinc.