We use Grodan and Cultilene rockwool products at work and generally soak them overnight in nutrient solution, adjusted to the pH it would be applied to the plants at (5.8). The pH does rise somewhat after the soak, on account of the residual lime left on the fibers after manufacturing. No idea about the particles though, we only use blocks and slabs.
__________________ Camille
Completely orchid obsessed and loving every minute of it....