First Grow - All Organic

Hey guys As you can see on this week's pics, this 5th week of flowering was quite frightening : for no reason, after a regular watering with nutrients, some leaves quickly showed some brown burns at the tips, but also in the middle for some of them. Both plants showed symptoms, and I was quite surprised as I did not feel like anything changed in the growth environment. Still my wife gave birth this week and I was bit tired, so mistake on my side is not to exclude ( but I water each pot with 4 x 1 liter bottle, so important dosing mistake shouldn't have happened ). I decided to give them a next watering without nutrients, but leaf burn and yellowing kept spreading, and still spreads slowly. I don't know so much what to do, buds still looking like they swell, but I'm a bit afraid this keeps on spreading, so I'm open to suggestions !