Bottom line is this, MOST growers agree that ph 5 is THE MIN and ph 7 THE MAX.
Then closing the gap a little more is the popular range of 5.5 - 6.5, and works just fine for SOIL AND HYDRO !
Finally we come to rest on the universal and neutral (grow wise) ph of 6.
You can never go wrong @ ph 6, but just stay between 5.5 - 6.5 at all times and you'll be fine.
If the ph fluctuates between 5.5 and 6.5, let it. The plant is causing this from eating.
But if it ever gets below or above those numbers, just adjust it back to normal.