Looks to me like Nutrient Lockup...this happens when one or more nutrients is at a very high level compared to the others. Too much of one wont let the plant take up others. This is also eminent with PH..If your pH is true high some nutrients wont be used and vice versa. At 6.5 to 7.5 all nutrients are available to the plant. If you start getting to Alkaline nutrients like Iron,Manganese,Phosphorus,copper,zinc and boron will become harder for the plant to use. If you get a more Acidic Ph Phosphorus and Calcium and Magnesium become restricted.If the Ph is too low (acidic) manganese can become toxic. Just some examples to help explain it a little better. Also soild high in Salts can restrict water intake resulting in droopy leaves. Hope this info might help...