If deficiency symptoms appear on old leaves, the problem could be from lack of nitrogen, phosphorus, potassium, or magnesium.
Deficiency: this has yellowing of leaves, from outside in, but with a dark green center vein, and curling of leaf tips, this is mistakenly diagnosed as nitrogen def or iron def a LOT. Necrotic spots form on lower leaves. Red stems. Leaves appear pale or
yellow. Stems and branches will be weak, easily broken. Affected plants are usually tallest and appear to be most vigorous.. too much sodium (NA) can cause a potassium deficiency.
Potassium is similar to Nitrogen and Phosphorus, has similar symptoms and has curling leaf ends when they die. Also the plant get stretched.
Add chemical fertilizer containing K.