Check the instructions which are freely available from www.miele.co.uk
or the relevant site for your country. Browse to the current models and you should find the PDF for your model. For non-current models, instructions are under the link "Customer Support".
In general, the instructions are as follows:
If the water in your area is very soft and constantly lower than 0.7 mmol/l (4 °d) you do not need to add dishwasher salt. The water softener must, however, still be programmed to correspond to the water hardness level in your area. (The salt indicator light will still come on, but should be ignored).
Important: Before filling the salt reservoir with dishwasher salt for the first time, you must fill it with approx. 2 litres of water to enable the salt to dissolve. Once the dishwasher has been used, there is always sufficient water in the reservoir.
Inadvertently filling the salt reservoir with powder or liquid dishwasher detergent always leads to serious damage to the water softener. Make sure you have picked up the correct packet of dishwasher salt before filling the salt reservoir!
Only use special coarse grained dishwasher salt for reactivation. Do not use other salts such as cooking salt, agricultural grade or gritting salt. These may contain insoluble additives which can impair the functioning of the water softener.
* Remove the lower basket and unscrew the salt reservoir cap.
* Fill the reservoir with approx. 2 litres of water (first use).
* Place the funnel provided over the salt reservoir and carefully fill with salt until the reservoir is full. The salt reservoir holds approx. 2 kg of salt depending on the brand used.
As the salt reservoir is filled, displaced water will overflow.
* Clean any excess salt from around the reservoir opening and then screw the cap on again firmly.
* Run the "Pre-wash" programme immediately to remove any traces of salt water from the cabinet.
For the Miele, the salt reservoir is usually under the bottom basket, the cap is usually grey in colour. [Only the latest models have the refill cap in the door itself].
You should be able to find dishwasher salt just about anywhere, I've even found it in Malaysia, sold at good ol' Tesco!! Brands of salt include Calgonit (Finish) & Somat.