Looks like a cal-mag issue. You could try adding more on that front. A few ml per gallon, or maybe an ec of .3 if you dose that way, would be a good place to start. Environmental conditions (very low VPD), incorrect ph, or issues with too much nutrients (eg phosphorus overdose) can also cause issues with cal-mag uptake so it's always good to check those as well. Happy growing! 👍🌱