Higher RH% During Night

I have been noticing that during the day I am running between 30-40% RH, however after lights off.. my meter appears to be going up to 70% RH. Is this bad? The only different being the lights are off.

All i can say is that in nature humidity is usually higher during the day and drops off during the night. I don.t know how or if it affects it adversely to have it the other way around.
Here is my favorite graph for future use:

Your day humidity is a bit too low and night is a bit too high.
You can decrease humidity by increasing the ventilation and vis versa.
try that



PS: are you flowering or vegging ? how far along ?

During bloom above 50% can be bad depending on variety.

I'm actually 40 days into flower.. I just checked and last night it got up to 80%. However, at the moment it is currently sitting at 44%.

nicougrik said:

All i can say is that in nature humidity is usually higher during the day and drops off during the night. I don.t know how or if it affects it adversely to have it the other way around.
Here is my favorite graph for future use:

Click to expand...

Actually rh increases during the night time in nature.It is most humid at dew point. Nice graph though.

nicougrik said:

Your day humidity is a bit too low and night is a bit too high.
You can decrease humidity by increasing the ventilation and vis versa.
try that

Click to expand...

Day rh is fine...no problem. Increasing ventilation at night would be very helpful..IMHO

i stand corrected

nicougrik said:

i stand corrected

Click to expand...

How cool! Thank you for not turning this into yet another RIU troll fest! LOL!!!

I like a guy who can admit when they have made an error...I do it all the time. Humility is a great thing to learn for cultivation...especially on online forums.

Try running a dehumidifier at night or more fans, but I found running a small dehumidifier helped me..

Well, last night when lights went off I replaced my oscillating fan with a box fan to test night time humidity. Overall, the humidity hit 55% throughout the night. However, when the light came back in the morning the box fan wasn't close enough to the light/canopy top, and the temperature went up to 108.

I replaced the box fan this morning with the oscillating fan back to how I had it, fixed position, angled towards the light bulb/canopy top. Temperatures dropped back to normal, 90 degrees.

What should I be doing? I can't switch fans, and running both isn't an option. I was thinking about running the box fan under the plants pointed upwards upwards, and then a small fan which clips directly to my reflector to blow directly on the bulb.

Thoughts?

We're not growing in nature, we're growing indoor. Indoor your lights will reduce humidity and during lights-off your humidity will increase significantly if you don't control it. The average is around 10-15% fluctuation between lights on/off (if you have controls in place) but it can be double that if you don't have controls in place like exhaust, fans and/or incoming air that's drier than your room.

Sounds like you're running with no fans/exhaust during lights off, you'll need to do something or risk mould, PM and the like in flowering. How quick and how bad depends a lot on strain/phenos but running 70-80% RH lights off is pretty well guaranteed that you'll get some form of mould.

I'm speaking from experience and data as I run wireless Temp/RH and other sensors that transmit readings every 15 minutes in all of my rooms.

Here's a reading from one of my veg tents, notice the difference in temps/RH when lights come on at 4:00 pm. Ok in veg, not Ok in flowering:

5/30/2016 7:33 PM 79.7°F NaN°F 60.0%
5/30/2016 7:18 PM 79.4°F NaN°F 60.0%
5/30/2016 7:03 PM 79.7°F NaN°F 60.0%
5/30/2016 6:48 PM 79.7°F NaN°F 60.0%
5/30/2016 6:32 PM 79.8°F NaN°F 60.0%
5/30/2016 6:17 PM 79.8°F NaN°F 60.0%
5/30/2016 6:02 PM 80.1°F NaN°F 60.0%
5/30/2016 5:47 PM 80.2°F NaN°F 60.0%
5/30/2016 5:32 PM 80.2°F NaN°F 61.0%
5/30/2016 5:17 PM 80.2°F NaN°F 61.0%
5/30/2016 5:02 PM 79.8°F NaN°F 62.0%
5/30/2016 4:47 PM 78.9°F NaN°F 63.0%
5/30/2016 4:32 PM 77.1°F NaN°F 68.0%
5/30/2016 4:17 PM 72.7°F NaN°F 74.0%
5/30/2016 4:02 PM 66.3°F NaN°F 76.0%
5/30/2016 3:47 PM 66.4°F NaN°F 76.0%
5/30/2016 3:32 PM 66.8°F NaN°F 76.0%
5/30/2016 3:17 PM 67.2°F NaN°F 76.0%
5/30/2016 3:02 PM 67.6°F NaN°F 76.0%
5/30/2016 2:47 PM 68.0°F NaN°F 77.0%
5/30/2016 2:32 PM 68.0°F NaN°F 76.0%
5/30/2016 2:17 PM 68.0°F NaN°F 76.0%
5/30/2016 2:02 PM 68.0°F NaN°F 76.0%
5/30/2016 1:47 PM 68.0°F NaN°F 76.0%
5/30/2016 1:32 PM 68.0°F NaN°F 75.0%
5/30/2016 1:17 PM 68.0°F NaN°F 74.0%

I have the same exact thing happen, hasn't caused any issues.
Keep good airflow with fans when in flower to help reduce the chance of bud rot, but other than that no big deal

Same boat buddy. Two weeks into flower and my RH lowest is 44% lights on highest is 67% right now lights off.

But I'm drawing air from my back yard and it's gloomy in so cal /:

Where you draw your air and vent out your air plays a big part

Anon Emaus said:

I have the same exact thing happen, hasn't caused any issues.
Keep good airflow with fans when in flower to help reduce the chance of bud rot, but other than that no big deal

Click to expand...

True enough, as long as there's no PM (Powdery Mildew) in your area. It's specific to areas so if you're in an area that doesn't have PM higher RH is Ok, even beneficial as long as it's not so high to cause bud rot. But if you're in an area where PM is prominent, it's always around, spores cannot be kept out of grow rooms short of stripping down every time you enter your room (not very practical). In that case what I've seen is that anything above 50% RH, regardless of how much air movement you have (I keep a mini cyclone going in my flower room), will allow PM to take hold/grow. So high RH can be a crop killer in certain situations like PM prone areas.

I initially found out about it when I moved to a new area and started growing indoor. It absolutely sucks and the best cure is prevention, keeping RH below 50% lights on or off is one of the best options. If I let my RH go above 50% and I have a new strain/pheno that is susceptible to it (usually only see this from seed, some are almost immune, it's my first selection criteria for keepers) it will get it and once it takes it's difficult to get rid of it short of an H202 bath. If I get it on an initial seed run I'll just trash it and move on.

More exhaust less RH.. In the past had a crop do this and finished product sucked from IDK what that smell was... Now I exhaust 1000+cfm in 175cf spaces... on timers and speed controllers until I can get it automated on a raspberry pi. RH never goes above 60 and I can keep it steady at 30-40% or lower this way if I want.