looked at the pics man. spotting looks almost like mite damage. check the bottom for small white eggs, if thats not the case there is a thread on plants issues in the forums. just search around bro. this screen is not the best for pics as im on the laptop at work LOL. Also was this a lower leaf? lower leaf drop is normal in the beginning of flower. If this is all over, then you need to consider a 50/50 mix of veg/bloom for a week or so to get your plants accustomed to the change, switching directly to bloom formulas can shock your plants a little and cause problems.