6 inch Air Carbon Filter Smelliness Control with Australia Virgin Charcoal, Built-in 14cm Fan Low Nois and Speed Controller, Smelliness Scrubber for Inline Duct Fan, Grow Tent 6" x 13.4"

You would need to seal it completely, because if you put the granulated charcoal and it covers 70% of the airflow, most of it if not all will just go to the remaining 30% as it has less resistance, air will always choose the path of less resistance. Would honestly be better to just buy a cannister with GAC and a ventilator on top, 6 inch cannister and 6 inch ventilator, 50 usd or so total, it can work for up to a year or up to 3 months if you have many odours in your house, very cost effective, the only downside is it is very very ugly setup, and that might be a big deal for you. like this one, it is a two-in-one cannister and ventilator 56 USD Actually looking at the design, well first and foremost it is almost a scam that it says it has GAC that removes odours, it has so little it works maybe for 2 weeks if you are lucky, smh.. Anyways, it seems the ventilator is at the top in the middle with a circular gap beneath and a cyllindrical filters surrounding, the best if you could DIY would be if you could frame it so you add another cyllindrical circular layer, like 4 pins of wood with a cyllindrical mesh, then you could fill it up with GAC. Second way is to put it right before the ventilator, in a square shape, but still leave space at the bottom for air, so you would need somehow to suspend it with a frame, but this way the air is first forced through the filters into the empty gap and it will seal as the only way out is up through the ventilator.