Anything organic will produce the food for the BB to maintain the nitrogen cycle without a fish/Betta in the tank....like live plants, shrimp, snails....etc....anything alive will produce the byproduct needed.....
The carbon itself is short lived/used up and can't be recharged-and the carbon needs to be changed per package direction if you want to use carbon. Using carbon is a personal choice and not needed IMO/E, however, having some fresh unused carbon on hand for emergency is a good idea-it has saved me more than once-but I don't keep it in my filters all the time.
The sponge part is good to use until its falling apart-but it needs a rinse/swish a couple of times a month or the BB will suffocate with the buildup of mulm/debris that it collects.
With the filter cartridge that are both carbon and sponge-you can either cut a slit and dump the carbon or leave it-Once the carbon is used up-its used up-but it won't hurt to leave it and will even provide more surface area for BB to colonize.
A lot of the BB are in the substrate, on the walls and on the decorations too, when you are dealing with really low bioloads- you usually can change out your filter media without issue, however, its always a good idea to monitor for spikes and make that extra water only changes if needed.
Also, you don't need to use charcoal and change your filter out all the time-its a personal choice-it won't hurt to leave the used up charcoal in the filter or you can cut a slit and dump it out saving the sponge part and giving it a rinse/swish a couple of times a month.
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