Problem

looks fine. exposure to artificial light can cause what you see in stems and petioles - probably correlates to areas of more intense light? low S can cause purple streaks in stems, but if you don't see coinciding symptoms, it's the light and no big deal. Could also be genetics. I've had purple trunk/stems - thoroughly purple not streaks. Again, if the typical coinciding symptoms of things that cause similar effects are not seen, less likely anything you have control over. If anything your plant is slightly overfed. the leaves don't have any clawing but heading in that direction. Keep an eye out for progressing excess N symptoms and dial back if necessary. Relative to a photoperiod, i'd wager that's just beyond 3 weeks of flower or thereabouts.