Advice needed please

Hi guys i've noticed some of my fan leaves have started to show signs of stress can anyone tell me what it is please and how to sort it out??

i'm growing in soil under 2 600w and on 18 hour cycle at the moment but want to change over soon as really,
they have been in the main tent for 2- 3 weeks from cuttings and tbh they did have these marks but smaller when they went in the main tent as smaller clones,
its not on every plant though i,d say about half of them and only on a few leaves which i have cut off now.

Whole plant pics are often necessary for diagnosis. Some possibilities would include incorrect soil pH, Mg deficiency &/or Phosphorus deficiency. The purplish look of the leaves is often indicative of P def. Damage between the leaf veins is commonly from Mg def. Wrinkled, deformed growth is often from high soil pH.