charcoal filter for box fan

ok guys, i have a setup i haven't seen yet. basicaly i got a 2x3 closet. the cieling is a shelf a cut a square in and mounted my box fan(average size large one, will meshure when light comes on)blowing up. it works great. keeps the closet 70-75 with a 400w hps. but my problem is smell and also light tightness. i was wondering if u guys think it would b possibal to built some kind of diy filter for it? any ideas?

get a carbon filter, inline fan and "scrub" the air

place some ona gel in a bucket outside the closet or room etc...

thx for the reply but the point is that i'ma do it diy. i got a plan tho. 2 furnace filters with charcoal between them. we'll see tomarrow when i get supplies

as above

ona gel is good stuff