Our filters have a very long service life, which means that the intervals between cleaning can be a few months or even years.
However, there is a clear indication that the filter needs cleaning: If the water level behind the filter mat is more than 5 cm lower than in the aquarium itself, the mat will allow the water to flow back much more slowly than the drive is pumping out.
If so, it's time to give the mat a thorough cleaning. This can best be done in a bucket with fresh water from the aquarium. Cleaning should only remove coarse dirt and restore the unhindered flow of water. It's important to get as many beneficial filter bacteria as possible, as they are able to metabolize and break down pollutants and waste materials.
Therefore, when cleaning, you should make sure that you treat the filter mat gently and not be too aggressive. After cleaning, you should drain the mat and then put it back into the filter.
You can extend the cleaning intervals even further with a little care. If you do your water change with a hose, you can use it to literally suck the mat from the outside. In this way, coarse dirt is regularly removed without reducing the number of filter bacteria too much.