I've never had a humidistat on my home humidifier actually sense the humidity properly so that's why we don't go the humidistat route. 

Does the system have a humidifier on it? 

We put de-humidifiers in our older homes that have humid basements.

Do you have a humidifier built into the system? 

Opening up windows will decrease the CO2 but it will increase/decrease your humidity and therefore you would probably want a humidifier/dehumidifier.

Do tenants use a humidifier?

Make sure your lease includes a clause that tenant is responsible for any damages caused by turning the humidifier off.

Running a humidifier will help solve the problem. 

Dont delete this moderators the life it saves could be yours...First The sources of mold problems in your home or office can be: flooding, leaky roofs, humidifiers, damp crawl spaces, constant plumbing leaks, excessive numbers of house plants, steam from cooking, shower/bath steam, wet clothes, and even your air conditioning system itself.MOLD can be very toxic ESPECIALLY Stachybotrys Chartarum ESPECIALLY a certain subset of the population.

There is no humidifier in question here.