Not sure if anyone reads this thread still or not, but I was wondering about using charcoal briquettes for this? I looked around online and although it's clear you wouldn't use it in aquarium filtration, it appears that it's commonly used by people to control odors in garages and storage sheds. I know carbon is relatively cheap when used for this DIY kind of thing as opposed to a prefab filter, but the amount of carbon to fill a 2gallon bucket is still a bit more than I would want to pay sadly.