The how to and why fors of CO2 supplementation for growers

[thirst4knwledge]

A grower on the Green House Seeds forum (dominicangreen) has a killer grow room and describes how he vents every three hours during lights-on and continuously at night. Also, while I realize his advice and books are somewhat questionable, Jorge Cervantes states in his latest book on page 322 that "Carbon dioxide-enriched plants still need ventilation to remove stale, humid air and promote plant health" and on page 326 "The room must also have a vent fan with flaps or a baffle. The vent fan will remove the stale air that will be replaced with CO2-enriched air." However, if there is absolutely no need to ventilate during lights-on other than for cooling, that information would certainly be helpful because it greatly simplifies enrichment timing. I am in the process of converting my 7'x8'x10' grow room to include CO2 with a Sentinel controller and I want to do it correctly.

Besides for emergency (high temps) and lights off ventilation while you're not enriching the air (up to you but isn't a true sealed environment), it is unnecessary to ventilate the room. I do agree with what Jorge Cervantes says about removing "stale, humid air", but the air in my room cannot be described by either of those words. I have multiple fans that serve multiple purposes (circulation, reducing risk of mold, promoting strong plant structure), so my air isn't stale by any means. Also, I use a dehumidifier, so my rh never leaves the optimal range. Last, I have an air conditioner so temps stay right around 85*f. If I didn't do those things, then I would definitely be ventilating my room, as I'd rather lose CO2 than lose my plants because of ridiculous temps, or mold cuz my air is humid and isn't moving around. But if you have these things, and you've got your grow room dialed in, you will never have to ventilate (except when indicated earlier). There is also something I read about recently called CEA (controlled environment agriculture). This is basically where you have a separate room that you vent the air from your grow room into, you scrub it, dehumidify it, cool it, CO2 enrich it, and send it on back in to your grow room. Completely sealed environment, and the only thing in your grow room are those big beauties. No heat from all that equipment in your grow room, especially if you're using something to generate your CO2. There was a 2 or 3 piece article on it in maximum yield, october 2009 issue.

 

[Mr-B]

According to George, He vents continuously during lights out because the plants don't produce enough o2 for health during lights off.



I dunno, I think George knows more than the average Joe about Co2 enrichment. No disrespect intended to Lazyman or the other members with different opinions.. I respect everyone and their opinions. My goal is to learn together.

Peace.
B

 

[sparkjumper]

George also says the best time to take cuts is a week or two into 12/12 which is another thing I've found to not work at my house lol

 

[Mr-B]

An article I found interesting. http://www.ahlgrows.com/documents/co2.pdf

 

[Lazyman]

According to George, He vents continuously during lights out because the plants don't produce enough o2 for health during lights off.



I dunno, I think George knows more than the average Joe about Co2 enrichment. No disrespect intended to Lazyman or the other members with different opinions.. I respect everyone and their opinions. My goal is to learn together.

Peace.
B

No disrespect taken, Jorge is a smart guy and is very knowledgeable, but I wonder if there's a couple wires crossed here.

because the plants don't produce enough o2 for health during lights off.

Well plants give off Co2 at night, and take in O2. During the day the plants take in CO2 and give off O2. My feeling on it is that the atmospheric O2 is sufficient during lights out in a closed/sealed room, but a means of O2 level monitoring would be required for testing either way.

Garden size probably affects this, as a small grow might not generate sufficient O2 and would eventually deplete it. Larger grows (more plant mass) would probably produce higher levels of O2 during lights on.

I'll see if I can find any research material on these levels in a sealed environment. Thanks Mr B!

 

[Mr-B]

No problem bro.

My new flower room is only 4x4x8 (128 sq ft) and I've sealed it very good.
From everything I've read, the plants stomata almost completely closes during lights off. This reaction causes less O2 to be released in the air, all the while Co2 is rising.

Plants need O2 for health right? so if the room is sealed and short of oxygen then venting fresh air into the room should be beneficial.

It's damn near impossible to seal a room 100% and those rooms with the smallest of leaks are probably have O2 leaking in, thus the plants seem to be fine. Having built my room from scratch, I went a little over board on the sealing idea.... hell, I filled the back of the electrical boxes with silicone!

I really appreciate all the help, Like I said, I want to learn together.

Peace

B

 

[Lazyman]

The only place on plants where they uptake O2 is through the roots, so I don't think high atmospheric levels of O2 are ever really beneficial, in fact high levels of O2 are toxic to plants, since it is a waste product to them really. I think an airtight grow would be fine on the O2 front, since the plants "exhaust" plenty of it during the dark cycle. Does that make sense?

 

[opt1c]

Garden size probably affects this, as a small grow might not generate sufficient O2 and would eventually deplete it. Larger grows (more plant mass) would probably produce higher levels of O2 during lights on.

speaking from experience, having grown with a sealed room with co2 for the past 2 years now give or take, a small garden will not generate enough oxygen to make up for that used by combustion of the co2; my burner would struggle to stay on due to a lack of oxygen which is scary because co2 is heavier than air and my burner does not sit near the ground. I had a concern that i was drowning my roots in co2; was growing in coco at the time. Lowering the ppm to around 800 seemed to fix the problem during early veg. Once the garden gets larger there is no problem with o2 and the co2 can be cranked back up.

if you have airstones in your setup pulling fresh o2 from a different room or outside might be beneficial

your room really has to be sealed for this to be an issue though

opt1c

 

[Lazyman]

Good point opt1c, for gas-fired burners this could present an issue with exceptionally well-sealed rooms, and if that were the case I'd recommend installing a ducted burner and putting the unit outside or in another room, and ducting the Co2 in (the water-cooled Hydrogen can do this.)

For air pumps, yes some models have a 1/2" fitting on the inlet so a hose can be run outside or to a non-co2'ed room, highly recommended if possible (especially since Co2 sinks and for air pumps on the floor, this could cause a prob)

 

[sparkjumper]

My pilot light has never gone out on my burner unless I turned it off myself.In theory it sounds like it could be a problem,but I've never seen anyone complain about their pilots extinguishing during dark hours here or on OG.The window AC and dehumid stay on during dark hours but I've never intentionally changed air in many a grow

 

[Lazyman]

My pilot light has never gone out on my burner unless I turned it off myself.In theory it sounds like it could be a problem,but I've never seen anyone complain about their pilots extinguishing during dark hours here or on OG.The window AC and dehumid stay on during dark hours but I've never intentionally changed air in many a grow

Just to play Devil's advocate, it would take significantly less O2 to keep a small pilot lit, vs a 24-36K BTU burner going full blast, but I think if O2 was so limited as to disallow combustion, you wouldn't be able to breathe in the room.

If you're ever in a sealed room and start getting dizzy/lightheaded, you've done an outstanding job of sealing the room and supplementing CO2! Until I hear of one instance of this though, I just don't think it's a concern.

 

[SkizOflan]

Hi, i've been following this thread as i'm dialing in my co2 in a new setup. Its roughly a 15x15 room with 4k lights and 44 plants in coco 5gal pots. Prior to doing some research on this subject, i had put a 20lb tank w/regulator in the room and used a co2 'sniffer' to get a reading from the air. I do not currently use any type of environment controller or fuzzy logic system to maintain my ppm's at 1500, i simply read the sniffer and adjust the regulator on the bottle to hit that mark. Obviously this mark changes on the regulator as the plants consume more c02 and i adjust it weekly as needed.
In my initial setup, i was venting in cold air thru the house a/c ducting which is controlled by a standard digital thermostat, thus my room was 'sealed' in every sense except the air coming in from the ducting. I did not calculate for this initially (rookie mistake) and found i had a problem when i was burning thru 20lb tanks every 3 days! So i began to troubleshoot the problem and installed a 19000btu(?) a/c in the doorway to a closet that is connected to the room so that i now use the closet as a hot chamber and vent the hot air from within this chamber up and into a space above the ceiling via inline fan + ducting. This solved the problem in a sense, because i was able to block off the central a/c ducting and use just the 19kbtu a/c thus preventing the dilution of my co2 with the central air coming in, but it created a new heat problem as the 19kbtu a/c cannot hold the room at temp solo, it needs the central a/c 'boost' to help it out.
So, my next step is to air cool my lights (obviously on a closed circuit) and see if that enables the smaller a/c to hold temps w/o the influx of air from the central unit so that i can maintain my co2 levels w/o dilution. In case i didn't mention, blocking off the central a/c "influx" did fix my co2 problem as i was able to bring the regulator back from about a 10 to a 4 and my tanks lasted about 8 or 9 days!
Any ideas on this situation are encouraged, but the real reason for my post is in response to the questions about venting out the air from the room at night time. I ask because when i went into the room this morning (after making some ventilation changes etc.) my co2 sniffer gave a reading of 4,256ppm!!! This could potentially be due to the 19kbtu wall a/c going out overnight (power strip breaker flipped) and thus rapid co2 concentration w/o any escape path (i assume some of it previously made its way thru the a/c to the "exit" ducting behind the a/c unit), but i think that the plants might also be transpiring large amounts of co2 during the night cycle and that's why i'm getting such high ppm readouts when the lights first come on.
For the sake of argument, let's assume that my a/c going off had nothing to do with the elevated co2 levels and that the plants were responsible. Is a ppm reading of over 4000 even possible from 44 plants (large! - 3.5ft) in a 15x15 sealed room overnight? Also, is it likely that i suffered some root strangulation overnight from such toxic high levels of co2? One more question, if i'm using a standard 24hr timer (the one with green and red pins for on and off) to control when my co2 regulator comes on and off, should i set it exactly with the 12/12 light schedule, or should i have it start a little bit before lights come on and finish a bit before they go off so ppm levels have a chance to come back down a little before lights out? Still working out the kinks, thanks so much lazyman all your posts are very thoughtful and informative, i look forward to all your responses and those from others!

Get Grown!

 

[Lazyman]

Hey Skiozflan, 4K ppm isn't toxic to plants, they just can't use the excess above about 2000 PPM's. Is your room hitting 85 with the lights and co2 on? If not please let it get that hot, your plants will thank you.

If you're going through co2 tanks that fast I'd say the room needs work, and you definitely need a controller. Right now you're probably wasting fairly significant amounts of your tanks.

What I usually tell guys is if your tank lasts less than about 3 weeks, a propane generator will be more economical. The water-cooled units will add co2 without adding tons of heat, and are cheaper than most "standard" generators too. I've seen them for $300 online, just run them on tap water to waste. A propane tank is $10 to refill, or $18 to exchange at Walmart, and usually lasts twice as long as tanked co2.

If I could talk everyone into getting a sentinel CHHC-1 I would, it controls the whole environment, including when CO2 runs (turns off when temps get too high) and can run a tank or generator setup.

 

[SkizOflan]

Thanks for the words of wisdom. It's always nice to hear from someone whose been there..

The room definitely needs work, but for now i've got the problem minimized. 83f day temps 1500ppm co2. A few questions:

If i'm running day temps between 80-85f, where should i want my night temps? And if it gets more than 15-20 degrees cooler at night, is this bad for my plants? I've been having some gnarly fluctuations in the past few weeks..

The humidity has also been above 50% as i've had to unplug my dehumidifier to get the temps down. I'm working on a solution (no holes in the walls!), but in the meantime what are some of the effects of high humidity on flowers/buds? It's been nearly 60% for a few days, is this slowing me down?

Also, can you tell me a little about the relationships among humidity, temp, and co2 ppm? I want to know what's going on with my co2 as the temp and humidity rise and fall, and how these environmental factors all relate, rules of thumb etc..

Get Grown.

 

[Lazyman]

Thanks for the words of wisdom. It's always nice to hear from someone whose been there..

No sweat man, glad to help.

The room definitely needs work, but for now i've got the problem minimized. 83f day temps 1500ppm co2. A few questions:

If i'm running day temps between 80-85f, where should i want my night temps? And if it gets more than 15-20 degrees cooler at night, is this bad for my plants? I've been having some gnarly fluctuations in the past few weeks..

Yeah about a 15-20* drop is nice actually, you'll find fairly dramatic purpling can occur with that exact differential. Keep an eye on the humidity with lower night temps though.

The humidity has also been above 50% as i've had to unplug my dehumidifier to get the temps down. I'm working on a solution (no holes in the walls!), but in the meantime what are some of the effects of high humidity on flowers/buds? It's been nearly 60% for a few days, is this slowing me down?

It slows down plant respiration a tad, but nothing dramatic. Growth would be largely unaffected. As you know, high RH is what tends to beget molds and mildews, bad stuff.

Also, can you tell me a little about the relationships among humidity, temp, and co2 ppm? I want to know what's going on with my co2 as the temp and humidity rise and fall, and how these environmental factors all relate, rules of thumb etc..

Well, that's a tricky one. Humidity is kept around 50% throughout the grow to encourage transpiration via a large root ball, and to reduce environmental mildews etc. CO2 is heavier than air so keep oscillating fans mixing it up, but generated CO2 will rise initially with the heat of combustion. Any gas-fired generator will create water vapor as a byproduct as well, which can effect RH, particularly near the dewpoint. Hard to hit dewpoint in a sealed and insulated room, but for you guys getting snow on the ground, it can happen with freezing air intakes. Notable condensation eh?

Get Grown

OK, wife said no more cheesecake, I've grown enough!

 

[Lazyman]

Oh, forgot to ask, why the heat problem? Are you running your lights during the night or the day?

 

[SoCoMMJ]

I had heard the myth of CO2 to kill bugs and did some research. Toxicity in humans is above 50,000 ppm.
http://www.inspect-ny.com/hazmat/CO2gashaz.htm

I'm pretty sure the 10,000 ppm won't kill the bugs. It's barely noticeable to humans at that level. Safe for 8 hours at 10,000 according to this link. http://www.health.state.mn.us/divs/eh/indoorair/co2/index.html

If anybody has actually killed bugs with their co2, I would be interested in the details behind it. I just don't think it's toxic enough at the levels we are looking at.

 

[sparkjumper]

Your breath averages 40,000 PPM.If you have caca breath maybe 45.

 

[Randybobandy]

If your regulator freezes its becuase of your tank. Get the alluminum tanks that have a tube inside that runs all the way down to the bottom of the tank. That solved my freezing. Now I can let it rip at full blast. I think 20 cfh. I had a grower freind tell me that co2 is uptaked the most in the first 2-3 hours of photosynthesis I get the co2 up to levels fast. Seems to help.

 

[sparkjumper]

Thats interesting I can tell you for sure that stretching plants will use much more co2 than plants after 30 days of 12/12 they use almost twice as much it seems