Nighttime Temps, Humidity, CO2 and Ventilation

Hey Guys,

I’m having some problems locating some good info on lights-out air control. I’ve got a 4x4x7 tent going with lights on 11on/13off (heard from DJ Short thats where its at!) with the dark period at night. My temps are perfect during the day, around 70-80, but at night with all the intake coming in from outside it gets too cold, 60ish and dropping.

I want to stop all intake/exhaust while the lights are off to keep temps around 65 while they’re flowering. I believe the plants will not need any fresh CO2 while they are going nighty night and producing 02? I will still have on some small fans within the room to stir the ladies up a bit, just no fresh air till the light comes on again…

One more thing… My humidity has been really low these past couple of days so I decided to hit the girls with a 2/3 strength Liquid Karma folar feeding. Should I skip the nutes and just continually spray water in the room all day? It didn’t do a thing to my hygrometer when I sprayed ‘em?.

Any advice, Q’s, comments?

THX

You shouldn't have to exhaust at night. My room is sealed with CO2 and at night I just don't run Co2 but the room is still totally sealed. I would keep it 65+ at night but that is just me. I know you can spray them with just water during veg if the humidity is low. Just during veg though. During flower they like less humidity anyway and high RH can cuase mold.

is it possible to use inside air for your intake during the night? will it shut down your filters too .. could be a potential smell problem if it does. as far as getting your humidity up .. have you got room for a pail of water ? put a fan blowing into the pail will increase your humidity a little, don't know about the foliar spraying, i would be worried about moisture retention in buds and causing mold after the 3rd week of flowering ... not sure if water sprayed on your hygrometer would effect it. sorry couldnt be more help

happy grown

I was under the impression that 11on/13off was a good idea too, but numerous veterans on this forum explained how having 13on/11off is a better idea early in flowering. The plants still produce flowering hormones, but have an extra 2 hours to collect energy from lights, meaning more growth. Makes sense to me.

As to your question, no you don't need co2 enrichment at night because photosynthesis has stopped. You have their biology wrong as far as what they're doing during dark hours. At night there is no production of oxygen within a plants body without photosynthesis, so theyhave to "breathe" oxygen much like we do. carbon dioxide is a byproduct and has no use at night(as it's a catalyst for photosynthesis) so it is released.

How low is your humidity? Don't spray water in the room all day, it will cause burn on your leaves if your lights are on, and plants only supplement through leaves, not replace their main feeding system (roots). Humidity takes time to adjust as well, as it's the amount of evaporated water, not condensed as you spray it. So after you spray, it basically has to re-evaporate to increase humidity. If you're worried about it, just put large surface area containers of water as closer to heat(lights) as you can.

tellno1 said:

is it possible to use inside air for your intake during the night? will it shut down your filters too .. could be a potential smell problem if it does. as far as getting your humidity up .. have you got room for a pail of water ?

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Yes, I could move my intake hose away from and close the window at night. Yes, it would shut down my filter at night if I keep it off. But now you guys got me thinking of shutting off all outside (cold) intake at night and maybe having my vent/filter come on 30min out of 90min. Its a monster for my lil tent anyway - till I upgrade my flower space

I have 1 150cfm and 1 250cfm inline blower fans as intake and a 400cfm exhaust pushing through a 800cfm filter… also 2 fans in the tent. overkill?


Mike, my humidity averaged 50% +-8% the first 2 weeks. Now, it is more like 10-40% with the average at 35%

Thanks for your guys insight!!!! No more LK in the spray bottle, introduce a bucket of water close to heat, close window at night, and run my filter 30 out of every 90min during the night. You guys rock!

IntrepidTraveler420 said:

Yes, I could move my intake hose away from and close the window at night. Yes, it would shut down my filter at night if I keep it off. But now you guys got me thinking of shutting off all outside (cold) intake at night and maybe having my vent/filter come on 30min out of 90min. Its a monster for my lil tent anyway - till I upgrade my flower space

I have 1 150cfm and 1 250cfm inline blower fans as intake and a 400cfm exhaust pushing through a 800cfm filter… also 2 fans in the tent. overkill?


Mike, my humidity averaged 50% +-8% the first 2 weeks. Now, it is more like 10-40% with the average at 35%

Thanks for your guys insight!!!! No more LK in the spray bottle, introduce a bucket of water close to heat, close window at night, and run my filter 30 out of every 90min during the night. You guys rock!

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glad i could help a little

happy growin

11 on 13 off should only be last week of flower you can herm a plant doin it rite away (trust me) 12/12 till last week it stresses the plant into finishing,
thats what dj means,,,Unless its some kinda pur haze then maybe but still i wouldnt till last 30 days(it might put plant in survival mode) male flowers+ seeded pot bro>>>>>

dp sux said:

11 on 13 off should only be last week of flower you can herm a plant doin it rite away (trust me) 12/12 till last week it stresses the plant into finishing,
thats what dj means,,,Unless its some kinda pur haze then maybe but still i wouldnt till last 30 days(it might put plant in survival mode) male flowers+ seeded pot bro>>>>>

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I’m taking that advice to heart! What Mike said too.. a gradual increase from 13/11, 12/12, 11/13 and maybe a solid 24 or 36 hr off right before harvest might have some strengths as far as stressing res production, I’ve been hearing. Though this is my first grow and I want to keep it somewhat K.I.S.S. I can be way overly ambitious sometimes and better just go w 12/12 all the way through this one. IDK lol maybe 11/13 the last three weeks… we’ll see. THX!!!

Get a thermostat ... My exhaust 6" inline fan is plug into a thermostat (the guy at the hydro store made it for me ,.. there is tutorial on how to do it yourself online if you are a bit of an electrician..) and so usually about 5 min after my lights go off, my fan stop for the dark time, I set it to 70, so in my case it works good, in dark period the fan only actually stops when the room is at about 67, then when the lights come back on the room is at 65 ( I might have to buy a little heater this winter when it;s colder in my basement ) then as soon as it reaches a few degrees over 70 it kicks in and my temps are stable for the day at 70. good luck

This is the one I have...works great...no brainer. http://www.growlightexpress.com/index.php?main_page=product_info&products_id=1134&cPath=93#googlebase

MOMAPUG, Some very nice pricing at www.growlightexpress.com ! Thanx

Wolfhound said:

MOMAPUG, Some very nice pricing at www.growlightexpress.com ! Thanx

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You are very welcome! I was trying to put together a list for a friend of mine that is getting started...all the little goodies that help, so I was looking for good deals

Having this set up works great....when the room chills down, the fan doesn't come on....when things warm up, it comes on as needed to keep the temp you choose dialed in.

Thx everyone! I’m going with that thermostat MomaPug!!! Will be the perfect addition for this winter!

I paid 30$ for mine

Endur0xX said:

I paid 30$ for mine

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That is an outstanding price! Link?

like I said I got it from the guy at the local hydro store ,.. he just made it like home made style with a regular thermostat, works great!