You definitely need to siphon off the dirt (called mulm) from the aquarium ground during every fortnightly partial water change. Special substrate cleaners are available to help you do this very effectively and easily. Fix the substrate cleaner hose on the bucket with the clip enclosed and the substrate cleaner the water will "suck in" the water until it flows into the bucket by itself. Then insert the gravel cleaner into the substrate using rotating movements. The substrate will be sucked in with the dirt but will fall down again due to its own weight. The dirt, on the other hand, will be sucked out. There is a suitable substrate cleaner for every aquarium height.
Deutsche Version: https://youtu.be/eCG_mx9XdBQ (JBL PROCLEAN AQUA EX - Bodenreinigung im Aquarium leicht gemacht)
English Version: https://youtu.be/CXnYWzt7B8A (JBL PROCLEAN AQUA EX - Substrate cleaning in the aquarium - the easy way)
Nederlandse versie: https://youtu.be/Ddotbkh0ftI (JBL PROCLEAN AQUA EX - Moeiteloos de bodem in het aquarium reinigen)
Version française: https://youtu.be/hpuvaExBr5E (JBL PROCLEAN AQUA EX - Pour un nettoyage facile du sol de l’aquarium)
You can find out more about the substrate cleaners of the JBL PROCLEAN AQUA EX range here: Čištění dna .
You can read more about water changes and substrate cleaning in the Themeworld Aquarium under: Výměna vody .