It the plant in the same container from the beginning of the flowering ? This might be a root bound issue. Check that out and keep us updated.
LuciferN Reviewed by LuciferN on . First Grow Using Scotts potting soil. indoor fluorescent. bout 5 150watt equ. about 2-3 inch away from plant lights on 70-80 off not sure. but it's off during the day. 12/12 light cycle Did not test runoff PH Sink water about 5quart pot. Rating: 5