the pH helps the plant absorb nutrients, so you can do the final flush with any pH. the mission is to remove nutrients from the plant. in coco, you can do it in 20 minutes, practically removing all the fertilizer. then just 48 hours of rest and you can harvest. now let me explain.. coco is an inert substrate, so without fertilizers, and if you don't add any, the plant dies. soil is a substrate with nutrients; it's active and can grow a plant almost without adding anything. so an active soil with normal fertilization will always have some, albeit minimal, nutrient load. a well-done flush in soil needs 3 times the liters of the pot; 11 liters = 33 liters of water for the flush, and in the end, you'll still have some nutrients. coco is simpler; in an 11-liter pot, 11 liters of water should be enough because the drainage in coco is greater. when I have the plants nicely loaded, I start 2 weeks before to remove nitrogen and gradually decrease until I reach zero. then I check the EC of the runoff, and when it's at the same level as the water I'm using, I wait 48 hours and harvest. lately, I've read that a flush shouldn't last more than 20 minutes because the roots would suffer; I don't know if that's true, but it doesn't cost anything to try.