roc wool P.H. 5.5?? is this right

I was wondering if the directions on my grodan roc wool cubes is right. It says to soak the cubes in p.h.'d water of 5.5 I thought p.h. should be around 6.4 to 6.7.Are new cuttings different will 5.5 ph help them root faster? any tips would be great as this is my first time. thanks guys.