i made some changes now its way better at about the same cost.6 inch duct booster fan was $26 got 2, 8 inch end caps $3 each. one for the bottom, cut a 6 inch hole in the other .have a 6 inch inside screen and a 8 inch out side screen a short 6 inch piece to go through the end cap you cut the hole in, to the inside screen about 2 inches in so all air must go through the carbon.fill the space between the two screens with carbon.i got mine from pet smart i think it was $13 a half gallon it took 2 of them.put the end cap with the 6 inch pipe going through it on.i used self tapping screws to hold it all together.put the fan on and go.with the ones i made for the lights.this is all i use and i smell nothing in here with 6 budding plants. ask away..i'll get back asap.