Link your questions to a diary! This will help us help you....
Check the pH of your runoff... it should be between 6.0 and 6.5... If you're feeding grow nutes, knock them back, especially in flower.... Do both of these and you'll be ok.
Good luck
Look like first sign of potassium deficiency.
https://loudclouds.co/wp-content/uploads/2016/07/marijuana-deficiency-chart-jorge-cervantes.jpg
Start feeding some more K.
Happy growing.