What are these spots and discoloration on the leaves of my plants

Got 3 NY Diesels, fem, all germinated the same day, 1 month since germ.
I noticed they're getting this discoloration on some of the fan leaves.
I've tried to maintain the humidity under 60%, around 50% avg.
I haven't given them any nutes.
I'm about to transplant in the next week or 2 and don't want any issues beforehand.
Oh n they are in soil. Miracle grow (I know ) I plan on transplanting into Black Gold, I just needed soil asap so I had to go with MG at the moment.
Any thoughts on what this might be?
 

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