They do make carbon based sponge filters but I have only seen them on ebay.
IMO carbon is kinda pointless unless for some reason you need chemical filtration - like my snail tank needs carbon otherwise the water reeks to high heaven 24 hours after a water change. i am not willing to change the water every day.
Not sure how well the carbon sponge would work because carbon only works for a month or so and then needs to be replaced.
SInce i have money again, I plan on getting 2 sponge filters for the divided 10G so both sides get filtration and water movement. Does anybody now if these type of sponge filters are any good? They sell for ebay for pretty cheap
or should I just pay the extra few bucks and get the hydor sponge? The LPS has Deep blue sponges but they are all too big-for 30 gallon tanks and up.