OK
To answer your flourite questions:
First of all when you wash the gravel I assume you have it in a bucket outisde with the hose..
Thats what I did. Now you simply cannot get the murkines out of it. You will wash and wash it, turn it and churn it, but the murky water stays. Just do it for a few minutes to get the dust out.
I initially layerd it down first (15.4lbs/7kg) in my 20gal, then covered it with 15lbs of tiny gravel. My fault was that the gravel was white and the flourite was black with some reds. It looked ugly in my tank. I decided to mix em up. I did a bit and some of the water got darker.
I am adding another bag (15.4lbs) of the flourite to total my gravel to 45.8lbs which is close to the recommended 2lbs per gallon (40lbs).
ANYWAY- the stuff darkens the water but your filter will take care of it within 24 hours.