There’s two ways to lower Relative Humidity:
1. Remove more moisture from the room. (Lower Absolute Humidity)
2. Raise the temperature of the room. (Increases the ability for the atmosphere to hold moisture)

With a temperature of 80° and a relative humidity of 75%, your dew point is 71.34°.

The first thing you want to do is find your dew point temperature outside your room.

If the dew point is lower outside the room than it is inside the room, installing ventilation for the light hours would remove more moisture. In other words, if it’s dryer outside the grow room then we can ventilate out the moisture that is coming from the transpiration of your plants, and replace it with the dryer dew point of the outdoors.

I say dew point because we need to take the dew point of outdoors with the temperature of indoors to find the relative humidity that you would have indoors.


A few bowls of rocksalt help to absorb moisture.

If it appears that the humidity in your grow room and the relative humidity in the outside air is about the same, exhausting the room and bringing in new air wont do anything to help your problem.
Tons of rock salt and a larger dehumidifier?

I dug on some more inforamtion:
Raising the temperature in the grow room will lower the humidity.
Have you thought about adding additional co2?

The reason I ask is....if you add co2 to the room, the plants will thrive at a higher temp, and the higher temp will lower your humidity.

Look at it this way:
With a temperature of 80° and a relative humidity of 75%, your dew point is 71.34°.

Now, because you’re using CO2 you could raise the temperature of the room to increase the ability for the atmosphere to hold moisture, which will lower the relative humidity. With the current dew point being 71.34° in your room, these are the temperatures and the corresponding relative humidity that you would have.

If the temperature were set to 75°, then the relative humidity would be 88.43%.

If the temperature were set to 80°, then the relative humidity would be 75%.

If the temperature were set to 85°, then the relative humidity would be 63.81%.

If the temperature were set to 87°, then the relative humidity would be 59.87%.

If the temperature were set to 88°, then the relative humidity would be 58.01%.

If the temperature were set to 89°, then the relative humidity would be 56.21%.

If the temperature were set to 90°, then the relative humidity would be 54.48%.

If the temperature were set to 91°, then the relative humidity would be 52.8%.

If the temperature were set to 92°, then the relative humidity would be 51.18%.

If the temperature were set to 93°, then the relative humidity would be 49.62%.

If the temperature were set to 94°, then the relative humidity would be 48.11%.

If the temperature were set to 95°, then the relative humidity would be 46.66%.

You can easily see how raising your temps could solve your problem.
Peace

Interesting, but since recommended humidity during flowering is 50%, would anyone really want to raise the temperature in their room to 90 degrees? That's a stressful temp for the plants!

Videoman must live alone.