If somebody could take a please look at my leaves. This is a sativa dominant 9 to 10 weeks flower I'm in week 5 to 6. If I had my own opinion it would be from too much potassium. I try my best to pH the water 5.8 to 6.5. not all of my plants are doing this.
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Looks like stress, not potassium.
Could be the light is to close. If the light is to close high temps and low humidity would increase the stress.
If you started from seed plants will have different levels of tolerance to these things.
That would be the place to start.
What type of light?
How far from the canopy of the plant is the light?
What are the temps and humidity?