I suspected as much-Il get rid of the carbon and add another sponge. The tank im talking about is my 21 g, ammonia and nirites are 0, and I do regular water changes/gravel vaccums.
So if I take out the carbon and add another sponge, with the original sponge and sponge on the filter intake tube remaining, the bacteria colony will be okay? From then on I only need to rinse out the sponges every so often?