i think that may be some sort of a pest problem. i could be wrong though. i can't imagine white spots being from any sort of nute/water/ph problem. i know in a sea of green they generally prune the bottom 1/3rd so maybe it naturally dies off? lol idk still on my first grow
if its powder mildey try to use serenade, it gets rid of that. and the bottom leaves will slowly die off, because they are of no more importance(all the nitrogen has been used)to the plant.