If your plants are like mine( 5 gallon buckets) you dont need to flush for 2 weeks.I flush for 3 days sometimes 4, my plants will drink almost 2 gallons a day at the end. What i do is drain all water in my res and run 3 or 4 gallons through just to get everything out of it and off the roots, then refill with 3 gallons of water and molassas at 700 ppm. then just let the plant drink that up and keep adding plain water until my ppm goes down to about 100 ppm,cut and cure, smooth as hell .Some people do the molassas for weeks but imo hydro is supposed to be quicker so why wait so long.