Ventalation during dark cycle

When flowering in a 12/12, how much air flow do plants really need during the dark cycle? There is no light on during this time so heat isn't an issue. Can I just keep the oscillating fan going and shut off the intake/exhaust in the dark cycle or is that going to slow down flowering?

If someone could give a link to some document that does a really good job explaining the primary chemical reactions during the dark and light cycles of a plant that would also be very helpful. What part of the plant uses which gases at what time and so on.

you want to keep the fans going to stop mold. Sorry no good links.

i dunno stumps, if he's got the oscilating fan on wouldnt it just mean it would be more passive intake and venting since the fan would suck air from one area and move it to the other and the air pressure should push old air out the vent and pull in fresher air not just as much as if the fans were all on? that should be more than enough air circulation to prevent mold imo. and if you have your humidity and heat low mold should not be a problem even if you shut all the fans off for the dark period.

i recommend you keep them all on if possible btw, its better than just leaving on only the oscilating fan unless your using c02. Im just saying if it was a must you could shut them down during dark and only keep on the oscilating fan if need be , not that you should.

I keep all my fans running 24/7. I was just thinking keeping the room fan on was beter then nothing.

i am running a sealed room so i have no intake/exhaust.
i do however stop running my co2 when the lights are off because it was my understanding that running it at night is not beneficial.
my 16" oscillating fan runs the entire time the lights are on and then for the first fifteen minutes of every hour during the dark cycle.
seems to work for me.

DubRules its good to know its working for someone. This is my first real setup and I still have a lot to learn.

High humidity currently is not an issue. I don't think I have ever seen the humidity get over 30% in either my flower or veg rooms. So I doubt mold will ever be an issue. I heard some place that plants actually give off some CO2 and stop giving off O2 during the dark cycle but that could be entirely false. That's what got me thinking, maybe I should turn off the fan during those 12 hours to save energy and reduce fan noise annoyance.

This is probably best posted on a different thread but im going to mention it anyway since darkdestruction420 brought it up. I am using CO2 but I am only giving it to the plants during the light cycle every 2 hours. The the intake/exhaust fans stop when CO2 starts releasing. They get 15 minutes of CO2 release time and 15 more minutes after the release until all the fans kick back on. The oscillating fan stays on at all times. If there is something wrong with this setup please let me know.

I had a little cfl box, i tried turning my exhaust off along with my lights at night, when i opened in the morning it was a hot humid mess, i think you will have problems with mold.

fendre said:

DubRules its good to know its working for someone. This is my first real setup and I still have a lot to learn.

High humidity currently is not an issue. I don't think I have ever seen the humidity get over 30% in either my flower or veg rooms. So I doubt mold will ever be an issue. I heard some place that plants actually give off some CO2 and stop giving off O2 during the dark cycle but that could be entirely false. That's what got me thinking, maybe I should turn off the fan during those 12 hours to save energy and reduce fan noise annoyance.

This is probably best posted on a different thread but im going to mention it anyway since darkdestruction420 brought it up. I am using CO2 but I am only giving it to the plants during the light cycle every 2 hours. The the intake/exhaust fans stop when CO2 starts releasing. They get 15 minutes of CO2 release time and 15 more minutes after the release until all the fans kick back on. The oscillating fan stays on at all times. If there is something wrong with this setup please let me know.

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Sounds good your co2 should be added when fans stop. with that said. I think c02 is a waste of time for most growers. The extra co2 is just not all that much help if everything else is not dialed in.

I tried shutting off my exhaust fan for the nights and the humidity was ridiculous when i opened the door my room the next morning. Just try it and check it the next day. Next time im going to put mine on a timer so it doesnt have to be on all the time.

smppro said:

I had a little cfl box, i tried turning my exhaust off along with my lights at night, when i opened in the morning it was a hot humid mess, i think you will have problems with mold.

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I had the same problem. I had my exhaust on for 15 min and off 30 during my 20/4 four hours of dark. I have a hum/temp digital therm that I have in top of my fridge, so I can always see what is going on down in the room. When the exhaust shuts off the humidity jumps from 58 to 98. I just keep it on now.

#1Raiderfan420 said:

I had the same problem. I had my exhaust on for 15 min and off 30 during my 20/4 four hours of dark. I have a hum/temp digital therm that I have in top of my fridge, so I can always see what is going on down in the room. When the exhaust shuts off the humidity jumps from 58 to 98. I just keep it on now.

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Yea you learn real quick that you need exhaust at night too.

The flowering plants are around 28" now. When the fans turn off for 30 minutes the humidity spikes way up 50-65%. I am no longer even considering the thought of turning off the exhaust fan when it is dark. If the flowers produce more/bigger trichomes when the humidity is low then it certainly doesn't make sense to turn off the fans for any long period.

btw thanks for all the replies.

so would you say the best way is to just run your exaust with your passive intake and turn off the other fans ?becouse here in cali my humidity hardly ever gets above 40-45 either way..on or off now that its fall coming toward rain time it may get a lil higher..ppp

exaust 24/7 is best imo. If humidity gets high keep inside fans going too.