Aquarium Filter Media
Filter media and foams are very important, they help to create a suitable area for biological bacteria to breed and break down harmful waste in the water preventing water quality problems. Over time media can become exhausted after a long period of use, and carbon for example should be changed over. Foams tend to last longer, but will also eventually need replacing, they compact over time due to the waste and rinses they go through.
We always advise not to completely change filter foams or media in one go, you are better to stagger it over a period of time, this gives you beneficial biological bacteria time to transfer over to the new media, then you can change the old media or foam for new ones, this will then be colonised by bacteria on the media you put in earlier.