Hello. I think the average to flush is a week. Some people don't flush at all. Some people over flush. I'm an over flusher. I flush for 14 days in a 10 week grow. So it's up to you. I would say, start flushing now. I use water and Hydrogen Peroxide. The mix is - 1 ounce of 35% H.P. to 5 gallons of tap water. or half a ounce to 2.5 gallons of water. I find the H.P. really helps with the Osmosis of flushing. Good Luck. Chuck.