Rezinator - How sure are you that leaf tip is light burns? Most of the light burn I have ever experienced or seen the leaf tips look different. They are white to light brown from burning, the internal temperature fries the leaf and the color turns more of a lighter color. Fungus mold is black or dark colored and I would guess that is more the case then light burn. Don't you monitor the temperature at the top of your canopy anyway? (like you should be)