Tip burn is caused by the nutrient level (PPM/TDS) being higher than the plant can handle. It is like putting a vacuum cleaner on the root system, the nutrients start going in reverse instead of going into the plant the nutrient goes away from the plant causing the leaf tissue to dry out. Tip burn starts at the tip of the leaf & in real bad cases spreads down the side of the leaf. Having the nutrient level to high not only damages the roots but hurts your yield. Tip burn can be caused by many things; like the nutrient level being just plain to high, as well as diseases, and root rot. If the root system is sick or not healthy the plant CANNOT take the PPM (Parts per Million) being as high as when it is not sick.