Yes, i prepared my rockwool cubes with acid water, PH 5.5, during half a day, saying 12h. The light is a 250 HPS for the moment, temp is 26 celcius, and the ferts are GH flora series. I use self made bubbler. The plants are 3 weeks old and even more and they have only one set of leaves after cotyledon. But the root system is growing quite fast in my opinion.
I check the PH of an unused rockwool cube and it seems to be very basic, PH 9 or more.
Fhydro