When I search the internet about this question there are many different opinion about the right interval to change filtration media in a regular freshwater tank.
On the packaging of different media filter, the interval to change the media seem to vary by a good amount. Of course, company producing filtration media are more interest to make profit than what is left in my pocket, so for them the more I change the media the better.
So far, I have never changed the filter media of my filter. About once a month I will take apart the filter and clean it in old water tank (from a water change). I will clean the sponge covering the intake (I got shrimp so no baby in the filter) than the different media from the filter (another sponge, a bag of small rock and the charcoal bag). To clean those parts, I rinse them gently in the water until there is not much coming out and then put everything back together.
I'm not really interested to ear about the charcoal since after about two weeks it don't really have any effects on chemicals but since I don't use any in the tank I don't need to have any filtered out.
So why should I change (or not) my filtration media?