Potassium deficiency, or potash deficiency, often presents with a brown scorching effect on the leaves. In addition to a change in appearance, potassium deficient plants are often more at risk of frost damage and general infection.
Brown scorching (where the edges of leaves present a burnt brown color. Chlorosis (yellowing of veins) Purple spots on the undersides of leafs.
Seaweed products are often used to both prevent and address potassium deficiencies in aquaponics systems.