idk man almost all my plants, once they reach a certin hight, the bo0ttom leaves just always seem to die off, usually yellowingm, then dryting out, then wilting, usually i tend to pull these leaves off, seeing as plants dont bud that low, and it will give the plant more strewngth to build the m,ain cola. if ur only seeing this on the bottom 2, 3 nodes i think ur good, but iof it moves up u have problems. if its not low N then it could be over water