leach the soil, by this i mean run water into the plant pot and let it cycle through for abut a miute, there may be mineral and salt build up in your medium, if you over fertilized, unfotunatly, it will hinder the overall growth and potency of the plant. also remove or cut of just the dead part of the sick leaves, this will stop any disease from spreading to thr rest of the plant.
FLUSHING is done pre-harvest or the last three weeks before you chop your crop. this gives a chance for the mobile and imobile elements(food) to move through the plant used for budding, do this for a clean tasting crop. it also allows for the bud to burn better, you want a white ash after smoking a fully flushed crop.