Yesterday it was 1 out of 4 plants in flower, today it is 3 out of 4 plants.
I googled "cannabis spotted leaves" and in threads where's the images matched, they all concluded it was PH(specifically high PH causing a manganese lockout) or reached no conclusion. Interestingly enough 5 weeks into flower was the most reported time
Last watering day, I watered with full strength nutes and cal-mag adjusted to 6.2 PH. That was 3-4 days before this latest round of spotting and yellowing. I suppose the PH in the soil could be drifting back up. For most of the grow, until I experienced the the spotted yellowing, I was watering at 6.4-6.6 because I thought 6.5 was optimum.
In a regular water, they have been drinking 4-5 liters with runoff. I didn't want to wait until watering day so I mixed up 0.5 liters per plant of full strength nutes and doubled strength cal-mag. I PH downed to 6.0.
Photos of the two tall girls (shoulder high, the other two are waist high) The buds are still growing. They look to run completely out of leaves before harvest if this problem doesn't improve.
The bud that looked great two days ago. The bud itself still looks good
Starting on two previously unaffected plants.