Hi All Can anyone tell me what the issue it is a v...

Hey there Northern DC bud, I see you're using NPK and an additive that's the carb liquid, but since you're in Pro Mix HP, actually you also need cal mag. you can tell it's a magnesium deficiency from the discoloration of the serrated edges of the leafs. Pro mix is some kind of potting soil that's not like soil at all actually. With the heavy light schedule the plant needs more Mg to regulate photosynthesis, so you need need to add calmag to the feed. Since you've already run out of cal mag, you might want to go ahead and make a spray right away, whatever the bottle says just in a spray works fine. twice a week the first week then once every ten days before lights on. I see you have a perfect environment so what happens is the leaves open their stomatas up, do this and you'll be golden, the problem should stop spreading right away and the plant will recover in ten days or less. Hope this helps ! 🚀