I think they last a long time, but depending on the frequency of your cleaning them, they can breakdown. Not all sponges are identical and they take the abuse of cleaning differently. I think you will find many have more than one sponge and clean them alternately to minimize effects on the bacteria preventing major cycles.
GST introduced the carbon in his post. I believe he made the assumption that you were talking about carbon. It could just be semantics. "Bio Media" is a broad term, defined differently by many people. So is the word "cartridge"; some have carbon, some do not.
When I think of bio media, it is a surface that has beneficial bacteria growing on it, to continue the nitrogen cycle. When I think of carbon, I think of a process to remove undesirable DOCs from the tank. True, you can help control them by water changes, which is much cheaper than carbon. But if your replenishment water has DOCs you do not want, the carbon will do what the water change will not do. Especially if involving discoloration from the tap. While depleted carbon can be a media for bacteria to grow on, and that is your goal, there are better forms out there.
GST introduced the carbon in his post. I believe he made the assumption that you were talking about carbon. It could just be semantics. "Bio Media" is a broad term, defined differently by many people. So is the word "cartridge"; some have carbon, some do not.
When I think of bio media, it is a surface that has beneficial bacteria growing on it, to continue the nitrogen cycle. When I think of carbon, I think of a process to remove undesirable DOCs from the tank. True, you can help control them by water changes, which is much cheaper than carbon. But if your replenishment water has DOCs you do not want, the carbon will do what the water change will not do. Especially if involving discoloration from the tap. While depleted carbon can be a media for bacteria to grow on, and that is your goal, there are better forms out there.
