In all honesty, when I did hydro, I never flushed.. Perhaps a day or so of just plain water, but that was it lol I think a lot of the reasoning was a lack of patience, more so than any scientific purpose.. Pot is still a little heavy this morning, so I probably won't have to apply again until tomorrow.. The good news, this is day 2 with no dead leaves, so I hope it's on the rebound!!!!