HELP...When Should I start my Flush?
What medium are you in? Noone can really answer that question correctly without knowing what you are doing first.
If you are in peat or coco or a soilless mix. I'd flush for minimum of 7 days, prefer 10-14 myself. If your in soil you can do the same.
Flushing is primarily important when your roots are in a soilless or soil based medium that has heavy salt, nutrient build up which you want to get out of their so your final product burns and tastes better/smoother. Since hydroponics your roots arent effected by sitting in and constantly absorbing salts and nutrients that are built up in the containers it is as important to do a long flush like growing in other mediums.
So, If you are growing in a hydroponic system I would just cut back all nutrients in half 2 weeks out and than just ph balanced water for the final week.