Can you help me settle a disagreement?

I started a project with a friend, and on our last outcomes we had some problems with mold and flowering times stretching weeks+ over schedule. We are running Co2 and using a 2 part fertilizer with an assortment of additives and stimulants. When in veg, they do great with good average temps., and humidity around the 70% range -- both uncontrolled except by the lights, and air intake/exaust.
The room they are flowering in is located in the same environment with only a permeable membrain blocking light so the light cycles arent effected.

In my opinion i feel if we need to run a dehumidifier on the flowering end then our mold problem would most likely go away and our flowering times would be better. Without the lower humidity in flower, transpiration is effected not allowing full benefit of each light cycle causing a slower flower rate and less potency.

If you can explain the importance of humidity and its effects id appreciate it.

What humidity ranges are optimal.

Here is why humidity is important in your Home!

Humidity is the concentration of water in the air. This is very important to consider even when inside the home. You should monitor the levels of humidity in your home to keep them from getting too high or too low. Now that many people spend more and more of their time indoors, it is important that the conditions indoors are healthy.

What are the risks? If you would like to avoid mold/mildew, fungi, viruses, dust mites, harmful bacteria, termites and carpet ants, then you should monitor the level of humidity in you home. All of these things breed in moist, humid conditions. A runny nose, itchy eyes, increased chemical sensitivity, throat irritation and headaches can result from the development of these things because of high humidity and dampness, or low humidity and dryness inside of a home. High humidity in the home can make it more difficult to breath, which can cause fatigue. Low humidity is bad for your eyes and skin.

If you have wooden structures in your home, they can be damaged by expanding or contracting with the changes in moister in the surrounding air. Furniture can crack, weaken and develop mildew if not kept at the right humidity. When this happens, a poor smell can develop if not taken care of. You don't really want small green organisms taking over in your living room, do you?

If you have high levels of humidity in your home, you might want to consider purchasing a dehumidifier to reduce the dampness of the air. Higher levels of humidity are likely in the summer months. You should plan to buy a humidity sensor to find out and keep track of what the humidity level in your home is. An air conditioner may assist you in balancing the humidity in the air during the summer. Lower levels of humidity are likely in the winter. Since this can also affect your health and cause dry skin and throat irritation, you should consider using a humidifier to raise the humidity to a healthy level.

Whether you live in an apartment or a house, you should get a humidity sensor, an air conditioner and humidifier. To keep you and your family comfortable and healthy, you should take the proper precautions to insure that the humidity levels are not extremely high and not extremely low. This will also protect your furniture. This is just a word to the wise, since you will probably spend most of your time indoors, if you are like most people nowadays.

Optimum temps and humidity are for veggin: 78F temp and 60-80 RH, and for flowering: 72-75F and 30-50RH, so yes, a dehumidifier would be in order for the flowering room imo, especially if you are having mold issues. My flower room stays around 25-30%RH in the winter due to very low ambient humidity outside and I have not had any mold issues, ever.

I completely agree with GaGrown too....most people have no idea how humidity affects their comfort in their own home. It works directly with the temps to keep you comfortable! Is your house too dry in the winter when you wake up and your nose buggers are like concrete and no amount of dryer sheets gets rid of static electricity? Get a humidifier! Temp of your house is good and warm, but you feel cool and clammy, and your windows sweat up on the inside until water runs down your windowsills? Get a dehumidifier! You have to bear in mind, if you're not comfortable in your house or grow room, your plants aren't either!