That chart just shows the optimum ph for the uptake of different nutrient elements for a plant...If you fall too far out of range it will be harder to uptake certain elements...

In flower I drop from 5.8 to 5.4 in the 4th week, then 5.5 in the 5th week followed by 5.6 in the 6th week followed by 5.7 in week 7

Some growers find that their ph raises a little throughout the week, so they start low...i.e.5.4ph, and let the ph swing upward to 5.8-6.0ph by the end of the week.

You can run your hydro nutes from 5.4 to 6.0ph with no problems, and most of the time if you are staying in that range then you won't see anything more than a slight deficiency from time to time at worst. peace