With the GH product I use flushing takes about 3-5 day's at the end. You change the water every single day; but the most important thing to do it to watch the PPM. On day one for example: Your water starts with 25-75 ppm of clean water. You adjust the Ph and mix in the florakleen now you are reading about 150 to 200 ppm at most. This is before you turn on the pumps (just the ph adjusted water and flora kleen) Check the ph a few times a day it will change on you often sometime. Day 2 before you change the water out check and record the PPM it will be somewhere around 500 or more Repeat the same steps you did on day one to change out the water. Yes you change the water everyday so you are going to use a lot of water. Now you may not need as much as you did when you went 7-10 days between changes so keep that in mind. For 40 plants in a drip system that normaly used 20 gallons of water can flush with 5 to 10 gallons of water. Day 3 check and record again the PPM before you change out. You will start to notice it will drop in PPM over the 24 hour period. This time it is probably around 350 to say 500 ppm. Repeat the same steps you did on day one to change out the water. Keep records of your ppm change at the start and again at the end when you change them out. You change out the water everyday and check your Ph several times a day there aren’t buffers to help keep Ph in check anymore so you need to pay close attention yourself. You keep up the changing out of the water everyday until you have less then 50 PPM change over 24 hours from what ever you started with. You can do one more flush if your Trichomes are not to amber just because; but you don’t need to. It’s just a good idea if you do this will make the plant use up even more stored chlorophyll and that is always a good thing to help speed up the cure time. That is a proper flush and the way I personally track and flush anything I grow in Hydroponics.