Are you asking for ideas as to why it's foggy?
It may well be that the colonies of bacteria you need in the tank are establishing themselves and that they've bloomed. That may be the reason for the fogginess. If so, just give it a few days to see if it goes away on its own. It should.
You said that your water checked out fine. Did you check it yourself? It'd be good to start monitoring it (you can buy test kits at your local fish store). I suspect that it may not be as fine as you were told. Given what you've described, your tank should still be cycling and establishing itself. Check
MissFishy's signature for a link that describes the cycling process.
What kind of fish do you have in the tank? Hopefully, they're hardier species.
Oh, and, welcome to the Tank!