Soak it in some white vinegar overnight. Scrub and rinse in the morning and it will look brand new.
If u have more than one wetside, don't let them touch each other. Almost impossible to separate without damage.
i will do 50/50 vinegar (5% white + Ro/Di ) i think is more safe and work as well, if u forgot the pumps on (vinegar) for few days , u may damage the magnet (swallow).