There is a difference between the PH used for growing in soil, and that of the PH used in hydroponics.
Proper PH for soil is 6.5 and is good all the way up to “neutral” PH of 7.0
Proper pH for hydroponics is: 5.8 However; Hydroponics is a little more forgiving. So the range of PH can vary in between solution changes from 5.5-6.1, without ill effects.