I can say I never have to use PH up. My water is well above 7 to start, and after I add nutes, I always have to add a few tsp of ph down. I add this to a fresh gallon of water and then to the rez. I don't think I've been having any issues. Then I top off daily with 2-3 gallons of fresh water, and usually another 3-5 tsp of ph down again. If I happen to get to low, I can just add another gallon of non-ph'd water and that raises it up. The res fluctuates between about 5.6 and 6.0 over 24hrs, but I feel like that makes sure the plants get the nutes that are absorbed below 5.8 and above. The nutes typically stay nice and stable or slowly get lower over the week, which makes me believe they are drinking properly.