give some more details about your set-up ie: lighting, temp, ventillation, etc. i see others saying overwatering which is verypossible going from what little details we have. i see a little bit of what looks like heat stress. i could be wrond but the leaves look slightly bleached on the tops(could just be the pic though) it just looks very similar to the way my clones did one time when my fan died for 3 days. good luck. remember, it's all about detective work.