Hey there , that's a magnesium related symptom probably due to a heavy light schedule, the light being too close or perhaps a lock out but that s doubtful you know it's magnesium when the leafs burn on the serraded edges with yellowing between the veins often starting with the oldest leafs first. You can probably pick up on the mag but if you want to fix the root cause decrease your light schedule (you don't want to hear that I kmow) . Hope this helps ! ๐