Unable to find which problem this plant is showing signs of. 1 plant out of 5 showing tiny brown spots along the veins. Just noticed it. Soil fed bi-weekly(Fox Farms). Plant has nice healthy green color, stems are green. LED 300W lighting 18hrs on. This plant is my largest. Light was at 12" and just raised back to 18" (grew quite a bit over last 2 weeks. Unable to post picture for some reason. Difficult to see the spots at first, showed up very well with flashlight beneath leaf. Unable to post pictures. Will add pictures as soon as I can.
Follow up. Plant is Gorilla Glue Fem strain 5weeks old. Soil is Fox Farm Ocean Forest. Soil feeding bi-weekly with Big Bloom. Adding Grow Big next feeding, both Fox Farms.
Doubt anyone can help without those. Meanwhile, you might look at this: Plant Doctor - Diagnose Your Sick Cannabis Plants | Grow Weed Easy
I've never seen you post before actually. And yes that's what my guess would be also, but you can't be sure with a pic like that..
I'd give it some extra cal/mag. I use the same soil with the same nutes and got some calcium issues myself.