Beginner's mistakes

Look like you might have a potassium deficiency, Potassium deficiencies in marijuana are somewhat common. When using natural fertilizers like guano, you have to take into account the fact that potassium is going to be the least abundant of the three macronutrients (nitrogen and phosphorus being the other two). A potassium deficiency might actually make the marijuana plants appear taller and more vigorous at first glance, but the bottom leaves might be dying. The leaves may also be turning a tan or brown color and developing necrotic spots in some locations. Chlorotic spots will start to show up as the deficiency persists. Slow growth and smaller growth are all possibilities with a potassium deficiency. Potassium is important in the transport of water and the development of buds later on. Even so, small deficiencies are really only cosmetic.