It is difficult to decide how often you should replace your filter foams, as doing so can sometimes upset your water balance. Usually, the frequency depends on the type of foam, the frequency of maintenance, and the level of waste in your aquarium.
Generally speaking, fine foams (yellow sponges) should be replaced every 4 – 6 weeks. Medium and coarse foams (Blue) can be replaced as soon as their pores start to become larger, which is a sign of damage.
When replacing filter foam, it is important to not replace the entire thing at once. Replacing filter foam also means removing useful bacteria that aid the waste conversion process. Replace a third or a half of your foam first, allowing the bacteria to populate the new foam, and replace the rest after a week or two.
When adding new foams into your filter, rinse them out in your existing aquarium water so that they can absorb bacteria and won't restart the filtration process.
Every 4 – 6 weeks for fine foams; once any signs of damage occur for medium and coarse foams.
To find out more about replacing Aquarium filter parts, see our blog post.