Each to his/her own, but normally you would adjust PH when you are mixing nutes. If you check your res and it's too far off, you can add some PH up or down, but be careful not to over do it. It's best if you can flush, then add the proper nutrients.

You could also buy an automatic doser, or make one like I did for less than $100 using the thread in the grow FAQs. You should be able to adjust PH and anything else in the res without lifting the grow chamber, or the design is flawed IMO.