Help me identify this leaf discoloration!

Im getting these weird purple/grey speckles on leaves and dont know why. Any thoughts?

3rd week from germ
Under LEDs
77F temp
57.5% humidity
Fox Farm Happy Frog soil
2 doses of Root 66 at 20% reccomended dose. Watering 2-3 times per week

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Really hard to see anything. Could it be the dust from your soil?