Hi! I thought I knew the answer to this...... my filter is a Tetra whisper ex 45 for my 29 gallon tank. It has a bio scrubber that never needs to be replaced and a carbon filter(supposed to be replaced once a month). I thought the carbon filter was what everyone was talking about with rinsing it in aquarium water and not replacing it unless it falls apart. Now I am seeing that they are talking about a sponge of some sort. But my filter does not come with a bag. What is this sponge and what is its purpose? What needs to be replaced, how often, and is my filter okay without this sponge? Also, when I do replace whatever needs to be replaced, will it affect my cycled tank, and make it do a mini cycle, or should it be fine? Thanks!