when you first come across a problem in your plants it is never due to a lack of a nutrient your supplying. its always a question of lockout or cascade. low humidity and low temperature(especially in the rootzone) will kill your plant quickly by causing a potassium deficiency. high sodium in the rootzone locks everything out. it would take weeks for a nutrient issue to take hold if underfeeding is the issue. the problems come when something is completely denied to the plant. low humidity, light too close or too far, over watering, low leaf surface temp, low water temp, ph and ec in rootzone. 95 percent of time its one of these