Potassium Deficiency in Plants Notes:
Potassium (K) is a macronutrient.
Symptoms: Yellowing between veins of leaf (Interveinal chlorisis). Reduced flowering/fruiting. Leaf tips can look burnt or black. Sources: Potassium carbonate or potassium hydroxide (pearl ash, potash). Notes: This will raise PH, so add Potassium slowly and test every few days. Warning: Heavy metals added to a closed loop system will ruin an aquaponics system.
Photo Credit: http://en.wikipedia.org/wiki/Potassium_deficiency_(plants)