buy a TDS meter, watch EC level of runoff water from start,flush with pure water either ph'd or not until EC drops to around 1.0.You can even flush until it read 600-700.From that point your soil will be very low on nutrients,you can keep feeding your plant at small doses until harvest. Or you can do this like a last feeding ,4-5 days before harvest and chop.Or you can extend the flush period by dropping EC value of runoff by only 0.3-0.5 at a time.This way you can do 2-3 flushes in last 10 days.Aim is to let the plant use what is left in soil.If they are seriously nute burnt,do an extended flush session taking at least a week.or they are still green and healthy looking,do a single flush 5 days before harvest and chop.and you don't need to flush if your leaves are fading to pale green already.my opinion.