You'll hear different opinions on flushing. If you're mid-grow, I see no reason to flush unless they were over-fed. If you're talking about flushing before harvest, some flush, others don't. Since cannabis packs on weight late in the cycle, I like feeding them a light mix the last couple of weeks. You can back off to mainly water in the last week before harvest or even do a comparison (flush one plant and don't flush another).