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Smell as soon as lights and fans go off

When my plants go into dark, I turn off my fans at the same time (my ambient is <= 65F) so they don't get too cold.

Just a curiosity to me though, when this happens there is a strong grass smell in my room for about 5 min then it goes away.

It has 2 120mM (90CFM each) PC fans as exhaust and 2 passive intake (and 1 oscillating fan inside).

There is currently no carbon filter or even light trap as they are in veg, and .. i'm lazy, got all the materials for light trap/carbon filter/(ona if required), just have to put them together lol.

My room doesn't smell ever when the lights or on, or after the 5 minutes of being off.

I'm not concerned, i'm just very curious as to what could cause this, because I mean with the exhaust fans off, what could possibly pushing the grass smell out, and why wouldn't I have smelled it when the exhausts were on lol, confusing


New Member
I am just guessing that you are leaving your oscillating fan running when your exhaust turns off, (you should) and if that is the case then it is most likely just that fan blowing the air out of your space. My guess to the reason it smells for 5 minutes then stops is because the warmer air will cause it to smell more and as it cools the odor fades. This doesn't explain why you can't always smell it but its my best guess. I would also suggest you get the carbon filter up and running as living around growing herb can cause your ability to detect the odor to lapse, I use filters on my veg and flower room, more is better in this case.
I don't keep the oscillating fan on when lights are off, but have been considering it now that my plants are a lil bigger. Low temps with lights off are just an issue i'm monitoring.

I have carbon filters and a jar of ona beads, I just need to build the light trap around the fans heh, and I r lazy :)

I also have a bitchin air purifier (IQAir) that demolishes pretty much any odor in my room heh

But yeh carbon filters are comin, been waiting for plant health to improve, which is has dramatically finally


New Member
HiTeh,do you monator humidity in your room?I would think shutting down the fans at night would really raise your humidity;I may be wrong.High humidity will cause your carbon filters to fail quicker than anything eles,(just something to keep in mind).Also i dont know how long your dark cycle is but how does your plants get fresh air like this?It may be ok while plants are small,but when they get bigger I would leave the fan on;maybee use a small space heater at night.Good Luck & Stay Safe!!
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New Member
air circulation key
24 hrs a day
whats mother nature do with the wind? mimic her, make it calm, windy, darn windy, and holy chit windy. youll be amazed, id refrane from the holy one in flower. it tends to shake things up but o what a suprise!
I just found out its not the circulation at all.

I turned the lights on during the dark cycle for a few minutes to do something inside the closet (the plants are young and in veg, so I can't see 5 min of dark interruption doing anything bad to them).

Anyways, when I turned the light back off, they emitted the smell again for a minute. Weird as fuck lol

I monitor humidity yes, but have yet to do anything to change it, its a bit low at 40-45%


New Member
HiTech if you want to work on your plants at night use any green light;plants dont see this,you can even do this in the flowering cycle without worry.GREEN LIGHTS are Awesome!Stay Safe!!
HiTech if you want to work on your plants at night use any green light;plants dont see this,you can even do this in the flowering cycle without worry.GREEN LIGHTS are Awesome!Stay Safe!!

Yeah I saw that on Jorges Cervantes grow DVD too. Good advice, thxs for info.

I usually try not to interrupt em at all if I can though, just had no choice that night heh.


Member of the Month: May 2009, Oct 2010, Sept 2017
Depending on your setup... Lights produce heat. Fans/ventilation carry much of that heat away, but the bulb (and ballast - don't know if it/they is/are in a separate area) is still going to be hotter than ambient. If your fans stop when the lights do, you'll still have a heat-source in the GR - for about five minutes or so, lol.

Try setting the fans/ventilation to run a few minutes longer than the light(s).
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