There are several Threads with complaints about mold, tips for removing mould, with quite a few 'this is what I do...' posts. Some of the suggestions are useful, some, however, completely disagree with the official Swiss advice.
If you have done all you can to resolve the problem, without success, and the owner of the building (or his representative) refuses to take action, the
Rental Association could be the next stop.
The Official Guidelines regarding the avoidance of mould are now given in two booklets for free. French, Italian or German.
Here, thanks to Ziger, the correct link for
the English version. Look on the right hand side for the PDF.
No-one has to follow these ideas, but the owner or his representantive ( Verwaltung / Regie ) may be less than impressed if you quote posts by anonymous EF members as the source of your wisdom.
Stadt Zürich has
info here (only German).