How do  I mix it? with the epoxy or hardener and for how long as the mixture usually turn cloudy aft mixing it with epoxy. Is it suppose to be that way

Yes, that's right. It would no longer be clear when cured. Any additive (including fumed silica) will reduce the clarity of the resin when cured, particularly glass bubbles which make the resin go a white-ish colour.

Matt Statham
Easy Composites / Carbon Mods - Technical Sales