that looks a lot like a mag/ cal def. ide wanna lean toward mag. i had this EXZACT problem happen and it was cause i was watering the ph just a tad too low. i was watering at 6.5 and appearently my meter was off. cal and mag both wont get absorbed at 6.4 and lower. hope this helps a lot bro. good luck and lookin good. when you do add cal/mag or fix ur ph, affected leaves wont recover. look to the new growth to see if its fixed. goodtimez