The little spots are from one of few things. Rather your plants are using iron from a deficiency such as potassium or magnesium in places it doesnβt need to stay alive. Usually from spraying leaves in lights on or other def. , or Your plants leaves are looking yellow because they are lacking nitrogen needed before flower. If you didnβt give enough nitrogen while in veg, itβs a 50-50 and I would use a 8-8-4 ratio during flower. Even though they donβt require much nitrogen during flower they still require a little. If they didnβt have enough nitrogen during veg, whatever nitrogen they do have left will get sucked in and that plant will die. To me it looks like a calcium issue because your preflowers have nice pistil formation. If the leaves only had crinkles on tips Iβd say nitrogen or potassium , but where there are black spots on your leaves, Its telling me that the plants are using its iron to stay alive. I would use some cal mag every other watering and since your in preflower I would switch to a 2-8-4 bloom or I would go some black magic 5-5-5 all purpose and make a foliage tea to spray the leaves since it has the needs and calcium the plants might of missed out on. Look to see if the black spots have a purple tone to them. If so itβs iron. Itβs not necessarily an iron deficiency itβs just use an extra iron and put it in places other than the roots. Good luck and I hope it helps