is your lamp strong enough??,you need to be at least 30watts lamp power per sq ft of growroom,best if you can get around 55 watts per sq feet,and also,your average growlight only penetrates so far into the canopy,although this tends for me to be from flowering onwards,they get so bushy the lights just not strong enough down there and nutrients are being channelled to the top where the source of energy is,leaving dead leaves and so to waste away.if this is in vegy then it could be something else,hope my opinion helps old son!!!