Is the humidity to high for lights off

When the lights are off the humidity was up to 87% every day. When they are on it was anywhere between 35 and 50%. I bought an 1100 CF dehumidifier it only lowered to 78% when the lights are off and still 35 to 50% when they are on. The room is 4X5X 7’ high. There are 4 plants, 7 days into flowering. 8 weeks old total.
The temperature stays consistent at 80 to 82 when lights are on and down to 66 when they are off

400 Watt HPS 15” above the plants with CFL side lighting, no cool tube. A 6" fan blowing across the bulb.

A 6" exhaust fan with carbon filter. The air comes from a separate room into the closet and exhausts through the ceiling into another room. This fan is only on while the light are on. I can’t have this fan on for the off hours because it is to loud during the day. The lights are off during the day and on at night.

There are 2 6" fans blowing across the plants 24 hours a days

This is my second grow. They are doing much better than the first grow.

Should I get a bigger dehumidifier? The one I bought is an Ivation GDM20.
Thank You

You answered 1 of your questions yourself. Humidity is stable when exhaust system is on. You need to find a way to keep this running off a humidistat switch; Turning the fans on when temps, or humidity gets too high.

If you have to buy quieter fans. In the long run it will be cheaper than investing in bigger and bigger dehumidifiers.

You need to keep it down under 50% in flower. I like 40% even better but I am judging by what efficiency your system can operate at. :slight_smile:

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agree with “latewood”

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When the closet was on the main floor the humidity was always low. Now it is in the basement it is very high.
The exhaust fan is a Hydroplanet 6 Inch duct exhaust Fan 240 CFM. I couldn’t find anything quieter.
I have extended the hours the exhaust fan is on. I also bought a better humidifier. I will need it for drying as they will be drying in the same dark closet.

Thank you for your replies


Hello my plants are wk 5 of flowering came home today my light period starts at 8pm when I opened tent humidity was at 99% it has dropped dwn to bout 59 and still dropping should I be concerned during the dark period

I have no idea how you would get 99%? I have that in my propagation Dome

could it be possible the gauge might have got wet or something

No gauge is attached to wall of tent could it be that I watered last night and didn’t drain runoff from pans

Many Growers useing hydro and have 50 gallon reservoirs in their tent, so something else is up buddy

I don’t trust your reading, for some reason something’s weird. Consider a propagation mat at 99%, it’s wet you can’t even see in, its wet top to bottom

unless your tent is wringing wet everywhere it’s not 99% I suspect something’s up with your meter my friend

Ok thks I hope so will pick up new one

I would check batteries and yeah there like ten bucks on Amazon, I go through them like nothing because I use in my propagation mats but yeah 99% is like raining wet. good luck, your plants look awesome by the way!

Thks for advice I hope that’s what it is

You have ultra high humidity in dark due to refusing to ventilate. Ventilation needs to on a humidistat 24 hours aday. You have to find a way. Maybe find a quieter fan.

When it gets colder you get closer to dew point don’t see a good pic of your sensor but make sure it’s a little off wall remember coldest surfaces will condensate first