The first step is to take action immediately and resolve the issue as quickly as possible. When matters relating to mould go to tribunal, and are assessed as the landlord's responsibility, it is likely the tenant would be awarded rent relief and moving vosts if the mould is severe and goes untreated.
Mould can be a health issue and, as such, requires urgent attention.
Dark mould is most likely the result of moisture in the wall, perhaps due to a leaking pipe or some form of water penetration if it is an exteriro wall. Some moulds can be caused by poor ventilation and this is the tenant's responsibility. As a matter of caution, your property manager should provide ventilation guidelines to the tenant and request that they implement these immediately if they have not done so previously. A specialist can be engaged to determine the cause, however some other steps should be taken first.
Report the matter to strata and ask if any other units have reported a similar problem.
If so, they may have commenced investigations and have some clues as to the cause. Strata would be responsible for arranging for the mould to be professionally cleaned of the walls if it is their issue.
Most importantly, work towards rectification quickly through a process of elimination and investigation.
Lisa Indge, managing director, Let's Rent