They look good. What you thought was burn looks like a phosphorus deficiency in that one leave. Since your adding it to your nutrients you should be good. It's not unusual for the oldest fan leaves to have nutes drained from them. It's a perfect time to defoliate. You can remove the leaves and tiny buds from the lower 1/3 of the plant. Your nutrients look good just keep a look out for signs of stress like the leaves hooking, curling under at the tips or yellowing/browning tips. Your buds should be putting on some size over the next few weeks. Good luck