can you use .

the guy at grow shop tells me that that , 4 inch duct fans cant be used with carbon filters is right or is he just trying to sell me a more louder and expensive fan . even the makers say not to use with carbon filters its one that go in the ducting will it work as noise is a issue.

I feel like those inline duct fans are kinda weak to be your main source of forced air filtration.

fit like im scottish how you doin bud , thanks for replin u could be right. i need a quiet way off maskin the smell from my tent without the loud fans ;got carbon filter but scared off using the vents tt 4 inch fan that igot with it.

You can't use a duct fan with a carbon filter. You need to use an inline fan (centrifugal fan) to have them effectively work.