Need some help with discoloration (Pics)

Been reading forums on RIU for a while now and haven't ever posted.

I've got a small grow underway but I'm experiencing a bit of a problem, maybe not. the leaves on one plant started discoloring before the other and it is only affecting one side of the plant. If someone with experience could take a look and diagnose it for me you might save my life.

I may have overwatered only slightly but I want these babies to be lush and green. Plants are starting stage of vigorous growth and I haven't added nutes.

Wanting to be as simple and organic as possible, so I put off nutes till I could get an extra opinion or two.
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