Increased CO2 vs decreased heat


New Member
This is my first post and my first grow. I am using hydroponic set-up from super closet: the continuous nutes in-the-bottom-out-the-top cycle with bubblers in each sq. 6.5 gal container.

HEAT is a bitch.
If I run co2, I cannot run the IN/EX fans, cause they'll suck out the CO2. The room gets 94 degrees F.
With SS chiller (think Wort) I can get the Reservoir to as low as 62 degrees, depending on water flow through the chiller.

Even so, the air temp is 94.

Enter Portable A/C (exhaust out of the grow room) 8,000 BTU, SoleusAir. With the ac set at 78, the room and the reservoir stays at, well 74-80, and the res. at 68-71,

QUESTION; which is better. Increased CO2 or a more controlled environment without any excess heat.??
The only thing I can think of is running the co2 alternating with the AC unit. 2hours on CO2 (with chiller running) with no AC. alternating with running AC to keep the ambient temperature lower.

I know that the plants can withstand higher air temps with CO2, but I was no able to keep the temp lower than 94, and the plants were beginning to show heat stress. For the last 3 days, I have turned off the CO2 and am just running the A/C. I do not worry as much this way.

I uploaded a couple of photos.


New Member
I was hoping of the 116 people who have read this, one would have some insight. I have elected to put the CO2 and A/C on alternating times. A higher flow rate will jack the PPM co2 quickly. The ac is set at 70 degrees F when it comes on for one hour. I am using continuous data logging of the temps, Humidity, PH, PPM on a dedicated PC. The plants are doing well. now 5 days of 12/12. I should be able to sex them soon.
I left them in veg for too long.
I'll repost when I have more data.


New Member


New Member
In my opinion, temp is more important because the natural presence of co2 in our air will be adequate but high temps would be more detrimental. It's a delicate balance but temp wins. I know super buds are due to excellent growing conditions and genetics.
I grow in tropical temps. Always above 85f. I cant grow monster buds with those high temps.
But a compromise would be to focus the co2 to the plants while you let the cooling system running. It would waste a good portion of the co2 but it's better than moderate levels of co2 and high temps. In this setup, you have slightly higher level of co2 in optimal temps. The only issue would be humidity and you're perfect.
Good luck


New Member
I´m running a co2 system in a DIY-growbox/0,35m2/0,35m3. Figured out(at my conditions), feeding 10min on 1500ppm, switch off co2, exhaust system off for another 10min(co2 stays in the box). From minute 20 start exhaust system running for 10min. So you can do 2 cycles/h. Controlled by a digital timer for the valve(sorry, no clue for right word) armatur???.
In the past had allways tried different setups, because had exactly same probs.
Now I have a rel. konstant temp at the tops ca. 31°/89F humidity 65-80%, but I have a very unusual air-circulation system, very effectiv, humidity was never a prob.
Maybe you could give it a try the way i do.


New Member
Thanks for sharing those photos as a solution. I was suffering from heat issue as well. I wasn't too much concerned about planting them, but they did grow up. But the quality and quantity was lame. First I thought about my carelessness, But a friend of mine tell me that the heat of my room is a big issue.


Member of the Month: July 2012, July 2014 - Nug of the Month: July 2012
Plant growth rate and health are based on a 3 way ratio with: Temperature, light intensity, and available CO2. When all 3 are these are in the perfect amounts the plants will be at top health and growth rate.

If your lights are not exceeding 1,100 micromoles/m2/s-1 then CO2 is really unnecessary and wont really add much difference to growth because not enough light under this is available to drive photosynthesis up. Around 1,100 micromoles/m2/s-1 the plants photosynthesis rate will actually decrease with more light added, unless CO2 is also added.

You could have optimal light and optimal CO2, but if the temp is too high or 2 low, photosynthesis decreases.

You could have perfect CO2 and temp, but not enough light and photosynthesis rate is lower, and extra available co2 is not needed.

Its a three way ratio that is important. But If I were to choose 2 things to be perfect, and one not... the CO2 would be of least concern unless you are hitting the plants with more than 1,100 micromoles/m2/s-1 because the extra CO2 would be not really used without adiquite light or temps...



New Member
A couple rules which could help.
1. CO2 does nothing when the plant is in the dark. Bring the temp a little lower during the last of the plants night, then at sunrise start the CO2 for an hour and the outrageous temps will take their time getting there. I have one grow with AC issues and I run my CO2 when the heat comes up because it helps the plant deal with it. Silica also helps your plants deal with the heat.
2. Remember if you are using your CO2 late in the bloom cycle it will actually hurt the plants. It will make your buds "fluffy" and they will lack that nice hard nug that you would get without it. CO2 is more for the veg cycle and the first few weeks of the bud phase. So don't even worry about running your CO2 late in the cycle anyway.
Good luck with your plants.
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