You can use the descaler supplied with the appliance or a liquid descaler based on citric acid. Never use a descaler with acetic acid, as this will damage the appliance.
When you descale the appliance for the first time, use the bottle of Durgol® descaler supplied. Fill the water tank with the entire bottle of Durgol® descaler (125ml) and 1 litre water. If you use a different descaler, follow the instructions on the package of the descaler.