I can’t keep my RH under control in my tent. If I have negative air pressure in tent do I have to worry as much about humidity. It’s been fluctuating between 50-70 depending on lights. When they go off RH goes up then takes awhile to come back down. There is lots of air movement in tent with intake fan and oscillating fan. Just don’t want mold I’m five weeks into flower
If you’re concerned about RH, I would recommend getting a dehumidifier to lower the humidity. Be sure to purchase one large enough to condition the entire room. Not just the tent. You’ll likely be venting it out. These to put out some heat so be aware you’ll gain a few degrees.
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On a secondary note - if your humidity is going up when the lights are off, it sounds like your ventilation fan is turning off with your lights. Your exhaust fan (at least) should be on all the time. You can turn the intake fan on and off with the lights, or leave it on all the time if needed.
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The exhaust is on full time and the intake is on timer to be on the 4 hours of lights out and several other times throughout the day
That may not be true. My ventilation fan does not turn off, but the humidity does spike at night. It’s the cooler temperatures, cooler temperatures can hold more moisture in the air.
I know if I want to solve my humidity issues, I’ll turn on the dehumidifier. @TommyBahama
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Tutorial on Relative Humidity: this is a measure of how much water can be suspended in an air volume at a particular temperature. The reason the RH goes up with a drop in temperature is because air will hold LESS moisture at a lower temperature. That’s where the word relative comes in. Dew point is the more precise measure but that requires a precision thermometer and a wet bulb etc which is tedious. RH is easy to measure.
So what is your ambient humidity in the room? Are you in a humid environment?
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Just to ease your mind if you didn’t already know. Humidity doesn’t cause mold, it just makes conditions better for it to spread. For your tent to get mold, a spore has to be introduced, not just high humidity 
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It always goes back to normal when lights go back on after a while
If you are only going 4 hours light off, I wouldn’t worry
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The timer wasn’t working on my intake fan lights off for almost three hours now and RH at 43 
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Yeah I stay clear of using dehumidifier in grow tent. I will use it to dry buds optimally but that is usually just when it’s raining that day. (55-65%)
I’d agree playing with fans and temps to get humidity ideal. Someone posted a chart for ideal rh over various stages of the life cycle of the plant and it was much higher than I thought it would be late in flower. Something like 60-70%. I always assumed 40-50%. Maybe it was @blackthumbbetty? I know he has lots of that kind of information handy
Here you go:
Seedlings 70%
Grow weeks 1-2: 60%
Remaining grow weeks: 55%
Flower week 1: 55%
Flower weeks 2-5: 50%
Flower weeks 6-7: 45%
Flower weeks 8-9: 40%
Remaining flower weeks: 35%
And, you can use this chart to help adjust for different environmental conditions:
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Thats it thank you kind sir @TommyBahama well done
Our tent is in the basement and the basement readings are temp floats 68-70 with RH 40-65% But In the tent the temps float 74-77 and the RH 69% to 73% I have a tower fan for airflow which is great and both passive air vents are open and one hole up on the side is open a bit to vent heat from lights. The tent really has it own environment, considering that anytime I check it it stays the same. So is this OK for the tent? I still need to buy another light to jump start flowering for right now everyone is slow. Lights are on a 19/5 timer one is a Vivosun LED VS1000 and I have two Burpee grow lights 4 flour surest bulbs over the new plants. % plants in a 4x4x5 foot tent YES it was what we could afford back in Aug. this year.
Your humidity is fine for the vegetative stage, but too high for the flowering stage.
You tower fan is a good thing to have for air movement. This contributes to stalk strength and helps prevent mold.
But - you need to have an exhaust fan in order to bring the fresh/conditioned air in and to exhaust the “old” air. The humidity in the tent will then be closer to that outside of the tent. Once you have an exhaust fan in place, close all those passive vents except for one. Exhaust you air up high on one side, and bring it in down low on the other side. This helps create airflow across the plant.
I care more about plant leaf temp than air temp …but both are important …so I use a VPD chart that accounts for both: VPD Chart
I have a exhaust inline fan with the carbon filter which I nay remove right now just to get more air moving. Being disabled I could not get that thing up on the bars support with the straps so I have it right inline with a vent hole in the tent vented into the basement via ductwork and filter. I figured to keep the opposite passive vent’s open and close all others and see because is the high RH keeping them from flowering?
Well I went down and the RH was 85% Crap I disconnected the carbon filter and turned the online fan on lowest fan speed and in 30 min’s we are at 68% and I can feel air moving thru the vent and the temps dropped to much and the heater went on just like it was supposed to.
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