My short CO2 experience

I have worked in the scientific world for 40 years, and most of this is common.
If you have no safety training using compressed gasses, understanding of gas properties, DO NOT TRY.

After some success with grows and upgrading systems, I decided to add CO2 injection.
It would be wise for anyone considering adding CO2, to at least get a meter, preferably a monitor controller, as you will probably want it anyway, when you see the real readings with bags etc.

You really need to know your data : guessing at temp, humidity, maybe; ppm co2, no.
Also, a monitor/alarm is outside the tent (code) to monitor air nearby for safe co2 levels.

My tent is 4x4x6 and to me seemed like a perfect size to try it on.
Bubbler DWC with 3 - 5 gal buckets, usually culling one bucket along the way to make room for the other two.
Each bucket nute temp cooled by immersion heat exchangers (wort chillers).
Light is TS3000W drawing 450w

I had read about sealing tents, using too much gas…
I just finished a 10# bottle after 2 grows(18 weeks). $20.
i have exhaust with carbon filters(2 - 4” fans), and intake fans with hepa filters .
The filters are key to “sealing the tent”.

I don’t have any special sealing on the tent. I have any unused ports plugged with some foam.

How much gas am I using? Pretty much what most charts included with gas apparatus suggest.
~1.5 to 2 minutes on at 2 cu ft/hr. This is .07 cu ft.
Using the controller out of the box, the logger shows that the 1.5 minute injection would hold for about 20 minutes.

my basement ambient temp is 65 in the winter and high of 80 in the summer.

When the exhaust fans are on, they exhaust the existing air in the tent, and intake outside air.
When the exhaust fans are off there is no positive or negative pressure.
The gas is rained down from a loop of tubing with boles in it above the plants.
While gassing, three circulation fans keep things moving inside the tent, but add no pressure.
The added .07 cu ft. adds some. I can’t count that small.
The charcoal filter on the exhaust, and hepa filter or charcoal on the intake will restrict
any gas from thinking of taking the hardest path out of the tent.
That reminds me, I may gaffer tape unused/rarely used zippers.
There is still the ambient air being pumped to the tent via the bubblers. 1-2 cu ft min.
I’ll do some tests with bubblers/ no bubbles with the plants out of the room.
Those results should help approximate amount of co2 inhaled by plants versus tent leakage.
At first with this set-up, the controller would dose the tent whenever needed; whenever the ppm were low.
I would run with the controller for about 3 hours, then exhaust the tent, and open to tend to plants.
During vegetation, the temps would approach 90Âşf and relative humidity mid 80%.
This is fine for the vegging plants as the co2 allows the plants to handle higher heat and humidity.
It’s almost like forcing the plants to do a triathlon instead of laying at the beach. Of course they get fed well and often. At the end of a cycle,
some leaves can be seen foaming a few minutes after ambient conditions return. Rainforest, dew, all nice for vegging, not for flowering.
So I got some bluetooth temp controllers for 2 for $18. govee These work with an app to report current, log temp, humidity, and alert limits.
Worth the price of knowing.

Flowering set up.

The temp/ humidity log shows the temp/humidity rise with co2 injection and may continue to rise with increased time.
To control the the situation:

  1. The gas will run 2-5 min or until limit. TIMER IS USED AFTER CONTROLLER. Exhaust timer is synced with gas timer.
  2. After 20 minutes, exhaust tent(intake/ exhaust fans on) for 10 minutes
  3. Loop- cycle again after tent is exhausted.

This kept the temp mostly below 80Âş, RH 60%
This winter, even lower temp >78Âş RH >50%

I am planning to upgrade to a T8 exhaust and a S6 intake fans to replace my underpowered ac noise machines.
At 1/2 speed the T8 ec motor draws less wattage.
The ROI would be a few years though, not as good of a sell as new gen lights.
More control of the environment, quieter. The next step would be air conditioning.


I am in the process of investing in the same setup. Could you recommend at quality regulator? I’ve been looking online, seen a lot of bad reviews, but don’t know if those were due to user errors (i.e. no Teflon tape). I do have some experience w/ compressed gasses such as welding and flame cutting.

At 450w, do you think you have enough light for your plants to fully process the CO2? Do you see a positive difference/result?

I do believe different strains require different parameters, so if it works, great. Just a little curious lol.

Do you use a VPD chart to get an ideal of where you would want to target your temps and humidity?

A lot of questions I know, sorry. Not on my first grow, but definitely integrating more processes vs popping a bean and running a light lol.

Your plants look great and I like the depth of detail you’re providing! Please keep posting! Peace.

Thanks for stopping by. I have a Titan regulator, haven’t had any problems. No teflon tape used. A plastic washer seals the gas. Unlike a welding set up, there is only a pressure gauge for the tank, a valve/flow meter and solenoid switch. I just checked pricing and it blows my mind how much things are going up.
I paid $75. The monitor/controller is probably the best thing to have if just getting into this. A co2 monitor, at least, to know what is going on. I can see readings of up to 1000ppm from just tending to plants for 5 min. So they do grow better when you talk to them. And noticing increases with things like a flame, water heater turning on. Taught me co2 bags were not the way I wanted to go.
Yes, I think a 450w led light is enough for flowering in my 4x4. I get 100,000 lux at plants with mine. I was getting results with less, 300w leds.
I see the most difference in late vegging and stretching. Almost watch them grow. Last harvest I gassed them till I flushed.
I’ve checked VPD charts, and it seems as though the plants follow the charts more than I do.
Different strains may require different parameters, but most plants love co2.
I’ll post more in a while . Thanks again

1 Like

Maybe I’m wrong but wouldn’t you need alot more light to benefit from the co2?

1 Like

Yes he does. He just hasn’t experienced the difference.


I thought so, it’s been awhile since I checked into co2 so again I might be wrong (old guy memory) but without enough light to use the co2 it will actually slow down the plants growth.

1 Like

On the opposite end of the spectrum, I have too much light and not enough CO2 lol. Running a hlg 650r but w/o CO2 full power is pretty much useless or am I wrong?

Kinda depends on how much space you are illuminating…

1 Like

5x5x6.8 tent

1 Like

Well your canopy looks great so keep doing what your doing! I should be setting up co2 in the next 2 weeks or so.

1 Like

That should be adequate light for a conventional grow but likely would need double that for CO2. You also do not want to run soil: plants can’t uptake enough to keep up with CO2 and high light levels.


How much more light for a 4x4 tent? I know the mars is not a 1000w hid, but these new quantum boards are pretty bright and can get very close to canopy. Not so good for trees. I don’t think soil could keep up either. As my old computer 101 teacher taught me, “the hardware never lies”. Always learning here. Thanks, peace.

1 Like

So like none at all or only 600-800ppm?

You have to look at luminous efficacy and output to determine the PPFD you are getting from lights. But like stated; you need something like 1,500 µmol/joule minimum for CO2. Half that for a conventional grow.

That means you will need to look at the actual specs on the light you are using to determine it’s output.


You might get to 1500 in a 1x1 area right in the middle under your 650 but once you get out of that it probably drops off pretty quickly. Most of what I’ve read says they are using 600w bulb setup with multiple hoods, or built LEDs with bars set close together in order to intensify every ft². That why there’s not alot of people using co2 in order for it to do any good you have to have a sealed growroom that has everything you need to completely control the environment and by the time you have all that setup the actual benefits are not worth the money spent on the equipment and the electricity to run it all.


Well I have a tent in a sealed room and my light hits over 1700 par in the middle…but if I can’t implement co2 then there will never be a reason to run at max at guess…I do have other lights from previous grows but never considered running them

Also currently my plants are tied down at about 43" away from light…idk…I’m thinking I still might get a co2 setup for when I expand my grow but I guess there is no rush until then


I cant wait to comb threw this at the end of the day.

Thanks Dude / Dudette


I usually only run my co2 for the first 4 weeks from light flip when plant’s are growing vigorously…
Other than that I really don’t see a need for it…
I run rdwc , so my plant’s grow crazy fast anyways in vegg , so its not really necessary to run co2 in vegg for me…
And I haven’t seen a benefit to running it past 4 weeks from light flip…
By the way , I use a propane co2 generator in a 10 x 16 room , if your in a tent I would recommend a tank for co2…


How much heat does your generator give off?