Burnt leaf tips are generally the sign of over fertilization but is generally displayed on most of the leaves. Is the picture extremely recent? If you notice a uniform transition where the other leaves are doing it I would bet thats the case. Slight fertilizer incompatibility may also lead to a few random color (necrotic) spots on foliage as well. Anyone unsure about fertilizer regimens, ie: unsure if they are overfertilizing or underfertilizing, would be wise to visually look for slight leaf tip color changes. Apply fertilizers at 1/2 or 1/4 recomended doses if you are using pre added soil nutrients or have fertilized regulary with solution. When leaf tips are just ever so slightly yellowing (and Im talking the very 1/8 inch tip of your fan leaves) it is a visual indicator that your nutrients are on track and the plant is extremely close to being full on nutrients and verging over fertilization. If they go further up the tip as your pics are showing and actually start to turn necrotic (dying, drying up, color changes) than youve gave them to much. At that point the plants will continue to exhibit this behavior from main fan leave to most all growing tips and may need to be flushed with water, though you shouldnt ever get to this kind of fertilizer damage if properly diluting your nutrients to doses less than recomended until a good balance is met.
