Be careful not to piss people off, especially when it's hot and humid.

During that time it was very humid and there were no Windows opened or air flow.

East Texas you see lots of hybrid grapes like Black Spanish, Blanc du Bois, etc that can tolerate the disease pressure, high rain, and high humidity. 

So, my guess is it's mainly due to the high humidity. but every contractor that came in and hear the word "mold", immediately add one more digit to their quotes.The reason I agree to fix it is because the tenant claimed "breathing" problem.

You can get alerts on high/low temp and humidity.

Siding is last, again take this time to insulate better with either foam board or blown in insulation.I live in wisconsin and with cold winters and humid summers, I see a good return on energy efficiency.

Humidity levels were 75% to 90% in the unit.  

Many tenants just leave the water in the shower, not take an extra minute to squeegee the bulk of it down the drain, and leave the bathroom humid instead of leaving the fan on longer than the shower lasts, don't clean frequently, and then they complain about mildew or mold.   

Now I really love my out of state market and even think I could probably live with the humidity to never pay CA prices for anything again. 

This includes operating your heating and air-conditioning system as appropriate to reduce humidity, using appropriate ventilation, limiting evaporation of water, promptly removing any visible mold, and immediately reporting to us any leaks or other water intrusion into your apartment or any visible mold that you cannot remove.