In soil you want to be around 6.5 and hydro 5.9 or so. This is the only time in a plants life where pH is not suuuuuper crucial. I don't really think there is a wrong pH to flush or cleanse with, reason being is that pH is most critical because of nutrient uptake. Different nutes get abosorbed by the plant at different pH levels, and when you are cleansing the plant you are not as worried about nutrient uptake as you are with providing clean water through every cell in the plant. Hope this helped, sending super great harvest Karma your way