neem can cause clogging of the pores of the plant,if u spray with neem or any substance really u should take 2 sponges and wipe down the leaves when u start to notice problems,your plants can suffocate.i would also buy a cheap humidty gauge to see if your current gauge is potentially giving u the wrong readings.do u have any mold anywere near your grow space? have u tried a sulfer burner?