if you look a little more at it some of says experiment ph ranges. the company i use adds a ph buffer to their product and it is 6.5. i have to do no adjusting at all to my water it goes to 6.5 it have been working for me for years and i am not going to change it now. but i am just showing that 6.5 is the best ph for soil.
we add the cal mag because if we take our ph down to low we block out other more important nutes. so it is easier to just suppliment the small amount of cal amd mag needed for the plant