FULL DISCLOSURE
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. 
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:
- The gas will run 2-5 min or until limit. TIMER IS USED AFTER CONTROLLER. Exhaust timer is synced with gas timer.
- After 20 minutes, exhaust tent(intake/ exhaust fans on) for 10 minutes
- 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.
