I suggest a longer flush (7-10 days). Reducing the nutrients very low, to 1-2ml/gal for a few days, then a few days before harvest to do a full on flush to leech any additional salts int he medium. Plants eat very little the last couple weeks. Reducing the nutrients that low isn't going to starve your plant, but allow it to perform basic functions while starting the process of breaking everytng down .Good luck and happy growing!!