im trying to draw up a sketch on paint right now, but i was thinking, you could have the fan blowing into the bottom of the coffee can, then having the exust running slightly upward and out. maybe by putting a 90 degree bend in the ducting coming off the bottom then run for about a foot to keep any unwanted activated carbon pellets from finding their way into a fan.

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all of my coments are for any plant species, and their specificity is not condusive to any one species in particular!?