Filter media question, will choose best answer?

Ok, I have a tetra whisper EX45 filter that has bio, mechanical, and chemical filtration. Will changing the filter cartridge out (filter bag with carbon in it) take out to much of the good bacteria or will there be enough on the bio filtration portion of the filter (it is a plastic cartridge with little brush like projections for bacteria to live on, this never gets changed). Im just worried that im gonna end up going through another cycle if I change the carbon and bag because its got some bacteria on it. Also, can you used different media in these filters? Like make your own cartridge with a sponge or anything? I don't really feel I need the carbon and a sponge wouldn't need changing all the time? I tried to find info on this on the net but got nothing. Any help would be great! I will choose the best answer (and thumbs down any jerks so if you don't have a relevant answer stay away).