Yup, been there before. When you use those pre-mix blends, you need to check the ph of the soil, the ph of the water, and use nutes sparingly until the plants look like they need it. Deficiencies can come from a low or high ph, or a lack of nutes, but since you used a pre-fertilized mix I am guessing ph. Also, is there chlorine in your water? This can cause that kind of damage as well. Are you growing indoors or outside?
Dude she looks very nice! Keep up the good work!
As for autos, I am running my first outdoor auto grow right now. They are small and love the direct sunlight. I have some journal entries on them if you are interested. Check out this thread at the very least. It helped me immensely on my grow since autos behave a little differently.
https://www.rollitup.org/general-marijuana-growing/199319-autoflower-thread-resource-guide.html
Peace!