Black stuff in gas from filter?

ok so im trying to fix a 02 bmw x5 3.0. it has random misfires in all cylinders. after a new crank shaft sensor and new plugs nothing has worked i check the fuel pressure 38 psi right were it should be. so i checked the fuel filter and the gas that came out had a black tint and had particules in it. i have pu fresh gas( 91 octane no ethanol) in it and will be changing the filter in a bit. my question is what would cause the gas to get dark and is there any thing els i should do be for start up?