I just did a ton of scientific type of educational reading on the topic of flushing and why so many people think about flushing in the ways they do, and why all of this is so misunderstood and all the history which goes along with this and so many other cannabis myths. First lets address the term "weed" because this term is seriously so misunderstood... A "weed" is any plant you do not want growing, I don't care if it is the world's biggest and best rose if it is in the middle of a corn field, to the corn farmer that is a weed and he needs to get rid of it. A long time ago the US Gov wanted to get rid of all cannabis and deemed it a "weed" as they really went to great lengths to destroy all cannabis naturally growing in the USA. A plant will do everything it can to survive in its conditions, but at some point when those conditions become to much it will die, the same as you and me... you can get sick and get well countless times, but that one time you get to sick... that' it... DEATH.
Now in regards to flushing the final week, the reasoning people do it is to speed up the time it will take to cure the final crop from the chlorophyll within the buds and for the other chemical reactions to take place needed to turn it into good quality bud. If you run the nutes high right to the point of harvest there will be so much chlorophyll left over in the plant it can take a couple more months or more to be able to properly cure the bud according to the information I was reading, thus by cutting off the nutes ahead of the harvest the plant hurries up and uses up those nutes thus speeding up the curing process for smokable bud sooner. Now if you go off setting the pH of the water the plant is getting during that time, you have already started stressing the plant the last week by not feeding it and now you want to stress it even more by not pH'ing the water. Perhaps you do not realize this, but the more you stress your plant, the lower you make your yields... so if you did what you are saying it would cost you end yield weight, but hey if that is your thing do it. However according to the professionals who wrote some really in depth reading I was enjoying, they say only by keeping the plant happy and healthy right up the point of harvest with proper curing will lead to the highest potency, best tasting, and the smoothest of smoking for your enjoyment. Yes this information has also been tested against others who disagreed with what this says and it was found to be true and accurate and the smoke was better in every way compared to the same strain grown and flushed 7-10 days ahead of its harvesting with lower yields.