Spots on leaves

probably some time two weeks ago there was a pH fluctuation which caused the symptoms to first appear, and it's resolved now but the inertia of the thing makes it so that it sort of gets worse before the symptoms stop spreading. Nonetheless you're at a heavy light schedule so your plant needs more magnesium that's what's causing the yellowing on the serrated edges of the plant's leaf. You should probably lower the light schedule as much as you're comfortable with , the consider spraying cal mag at 1 ml / L twice a week just before "sunrise" for the next two weeks. Absorption by the leafs is 80% compared to 20% at the root level. You can probably increase your calmag to 1ml/L in the feed as well. Hope this helps ! 🚀