Question about Rockwool ?

I am about to put my seedlings that you are in one inch cubes into the 6" cubes. What PH level water should I soak the Rockwool cubes in before butting the seedling in it ?

5.5 ph is the soaking PH

i ph all my rockwool ,starter cubes,blocks & slabs at 5.5 & i use recirculating program [gh-floranova] i fill my res. & set ph at 5.5 then top off &reset ph when my runoff climbs to 6.6-7.0