If deficiency symptoms appear on old leaves, the problem could be from lack of nitrogen, phosphorus, potassium, or magnesium.
Deficiency: Slow or stunted growth! slow leaf growth, slow root growth, slow germination of seeds, slow bud production, red stems, the edges of leaves will be brown. Even fan leaves, the plants solar cells, will be affected by this, the lower leaves of the plant will begin to darken to a dark green, purple and blue color. (not the kind of purple you want.) Lower leaves yellow and die. And then the plant may begin to die if left untreated.
Add chemical fertilizer containing P.
Affected leaves will not show recovery but new growth will apear normal.