The small Whisper I recently bought is a single piece filter. If it were my filter I would, for the time being, rip the carbon out of the filter pack. At the same time I would stick in an extra piece of foam or sponge cut to fit in the filter. In a coupel of weeks this piece of foam will become full of good bacteria and you can keep that in your filter all the time, adding new catridges if wanted but you will always have a bacteria source that isn't dependent on the carbon.