yellowing of the lower leaves is usually a sign of nitrogen deficiency, while burnt leaf tips indicate 'burning' from over-fertilizing ... whatever source you are using for nitrogen, dilute it to half-strength, and spray it on both sides of the leaves (foliar feeding) for a couple of days, and watch to see if it helps ... don't be afraid to flush the plant when you suspect over-fertilization, flushing won't hurt the plant ... :smokin: