Very Low CO2 levels when adding yeast based CO2 generator

This has me puzzled. I have a grow tent approximately 4x3x7 feet. I’m growing one plant under 1000 w equivalent LED light (note: this is my first grow using LED. Previous grows I’ve used a 400 HID light). I’m using General Hydroponics Flora Bloom nutrients. I’m in the blooming stage so I’m mixing for aggressive blooming (1,2,3 ratio). I use a SOG grow method. I monitor CO2, RH & T using a no-name brand monitor. My bloom times tend to be slow so this grow I wanted to increase CO2 levels so I first attempted to make a yeast based CO2 generator from a DIY youtube video but it didn’t seem to generate any noticeable CO2. I next purchased a Grow Bro yeast based generator. The first 2 attempts didn’t increase CO2 levels. Next time around it raised my CO2 to about 1000 ppm. My next did nothing. On this last attempt not only did it not increase my CO2 but it made it drop like a stone. I currently measure about 48 PPM which is hard to believe but removing the sensor from the tent and putting it in my living space it reads about 450 PPM as I’d expect in natural air. I’m growing with my tent door closed. Previously with the HID lights I kept the door mostly open to dissipate the heat. So that’s 3 variables to troubleshoot past. The other symptom I have is trying to keep my ph up. I measure ph using and Extech EC510 water quality probe. It measures Conductivity, TDS, Salinity, pH, and Temperature. If I don’t add a ph up solution almost daily the ph will drop into the into the mid 4 mpl and I’m not sure how far down it will go. In the growing stage (using the aggressive growing nutrient ration of 3,2,1) it eventually stabilized to about 6 mpl).
So, to sum up:
Environment and Equip.
* 4x3x7 foot tent
* 1000 W equivalent LED light. Lighting on 24/7 in grow stage, 10/12 blooming
* SOG layout
* 5 gallon hydroponic bucket
* Using 2 air stones
* General Hydroponics Flora Bloom nutrients
* I use and have always used tap water. My tap water ph is 7 mpl.
* Grow Tent is in my basement.
* Fan circulation
* Temp runs about 21C

* CO2 dropping to around mid to high 40 ppm when adding CO2 from Grow Bro Generator. Without adding CO2 it measures about 480 consistently.
* ph reducing into the mid to upper 4 mpl unless adding a ph up solution then mid 5 mpl (note: this is independent of added CO2).

* Change from 400 w HID lighting to 1000 w LED lighting
* Adding CO2 (well in reality removing CO2) with Grow Bro
* Keeping grow tent door closed.

I think that is about all the information. If anyone has any explanation for this behavior and or a solution I’d appreciate any help you can offer. Obviously I’ve removed the Grow Bo.

Few questions do you exchange the air in your tent with some sort of duct fan if so its defeating your purpose its blowing your yeast created co2 out and bringing in ambiant… 400 is around atmospheric which is higher then ever in the past to be at levels 450 sounds like your co2 is being takin out of the tent and being shot into your house be cause 450 is higher then usual… yeast co2 producers dont produce that much co2 really second when say SOG …do you mean growing the single plant in a net because sog is multiple small plants to get same effect as 1 big flat plant…an even canopy is the goal in both but if you got 1 plants its not a sog u probally talkin about a scrog

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Hi Fano_man,

Thanks for your quick reply. No duct fan. I have a 6 inch computer case fan on the bottom of the tent against one wall and pointing about 45° up. So its below the canopy blowing upward just to circulate air.

Re SOG: Sorry I meant SCROG.

I’m not saying its out of the question but my tent is in a basement about 20 feet from upward staircase. There is closed door to the basement and my atmosphere reference point is another 20 feet away from that door. So I think its somewhat unlikely that CO2 is affecting the upstairs reference point. Add to that the CO2 is heavier than the atmosphere. As I said, I could be all wrong. I have an open mind so I don’t rule out anything. I will repeat my tests and report any changes.

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Sealed environment with a plant inhaling CO2 with a non working CO2 generator is no wonder your values are low inside the tent.

As a professional distiller I am amused by the sugar water/yeast generators: not going to do the job in that space, sorry. Compressed bottled CO2 is not particularly expensive (the gauges are though) and would do a far better job of getting the PPM’s up in your tent.

What is “mpl”?

Can you fill out this support ticket to see precisely what you are using? Please include details on your light as it raises a red flag to hear “equivalent”. My guess is you are actually running 250 watts or so. That being the case; CO2 is not necessary at all.


Are you attempting to use co2 to speed up flowering?

I use propane co2 generators…
In a 10x14 room… with great results…
I dont really believe in those co2 bags that they sell…
Or yeast generators…
They never work as claimed , unless your in a 2x2x4 tent … anything bigger then that then they are b’s… not gonna work…
That’s just my 2 sense…


Also …
I only use co2 in vegg and 1 to 2 weeks into flower…
But really only in vegg… just to get quick growth… then into flower and no more co2…
No benefit in flower that I can see…

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Hi Myfriendis

Seems a bit odd that it would drop the CO2 that much but you probably know more than I. If I remember my high school biology right don’t plants release CO2 at night? I would think that would offset a low value. Perhaps not to normal levels but i would expect some. I’m considering getting tanks for my next grow. I did see a regulator system for around $35, I’m sure isn’t great and I’ll do some research before I commit but I live on a fixed income so I often have to compromise or not do it at all. Hence trying yeast first. I’m hoping a small tank will go a ways in a small space. If so I can probably start out doing it right.
MPL = Moles Per Liter. Again if I remember my high school bio. I believe that’s the unit of measure for ph


Actually I’m hoping for greater yield. I have read reports that it does amazingly at increasing yields.

Adding CO2 can increase growth and yields assuming everything else is optimal. @TDubWilly is running supplemental CO2: he may have something to say. I do know it will do no good unless you are pushing insane light levels (which is the reason to push CO2 to begin with).

Did you find the specs on that light?


I see your point. I suspect you are right re: flower stage. I don’t believe buds absorb CO2. It’s probably useless setting something up now so it gives me a chance to gather equipment over the next couple of months.

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Well you’ll get no argument from me now that I have empirical results.

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Sorry, didn’t see the rest of your question it was covered by the text panel. I’m not sure I understand what support ticket. Did you put a link to one, do you want me to start one, or is this the “support ticket” which I’m sure it isn’t.
Re: Light. Here is a link to what I bought.

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COPY/PASTE the below list into your forum post.

Answer these simple questions the best you can.
If you do not know, or do not use something; Just say so; Or post
NA (non applicable)

  • What strain, Seed bank, or bag seed
  • Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
  • Vessels: Pots, Grow beds, Buckets, Troths
  • PH of Water, Solution, runoff (if Applicable)
  • PPM/TDS or EC of nutrient solution if applicable
  • Indoor or Outdoor
  • Light system
  • Temps; Day, Night
  • Humidity; Day, Night
  • Ventilation system; Yes, No, Size
  • AC, Humidifier, De-humidifier,
  • Co2; Yes, No

Always try to upload a clear picture of any issues you may have to allow the community to assist you.

Add anything else you feel would help us give you a most informed answer should be included. Feel free to elaborate, but short and to the point questions and facts will help us help you in a more efficient manner :slight_smile:

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FYI that light consumes only 120 watts or so. It is not sufficient to flower off one smaller plant, much less the space you are in IMO. @dbrn32 is our light guy but you need to be in the 35 to 50 watt per square foot range, from the wall and not what the “equivalent” is. (We’ve all been deceived by this marketing)

You would likely be better off to go back to your MH/HPS as it’s an honest output.

Higher end LED’s can bring the watts per square foot down to around 25 watts or so as the efficacy is much higher than that older tech.


I guess I’m not understanding why you’re not just running an exhaust fan? Even with passive intake, ambient co2 will be plenty with the light you are using. You are definitely not lighting your space enough to require more than ambient co2. Despite whatever manufacturer claims, that light doesn’t have anywhere near the par levels a 1000 watt hps has.

Plants need light, water, and co2 for photosynthesis. Increasing one without the others just creates a saturation point of whichever is increased. With 12 ft², you would need probably 5 of those fixtures to justify supplementing co2. In which case, just circulating fresh air through it would be more than enough for you. The co2 may be a problem without fresh air, but weak lighting is also contributing to slow growth.


Hi dbrn32: I understand your point completely and absolutely agree. I’ve changed back to my 400 W HID, just making new brackets now.
I will follow up this post announcing that I believe the problem was and is with the sensor. At the moment it reads 0 no matter where it is. i will post that separately in case others don’t read other’s replies. I didn’t realize until pointed out how bad the efficiency of this unit is. I’m embarrassed that I didn’t do the calculations myself as I’ve worked with electronics most of my life. I just took the word of the mfg.

Thank you again.



Thank you all for your help and guidance. The problem appears to be with my CO2 sensor. This AM it read 0 obviously not likely. I moved it from tent to upstairs living room and still reads 0.
I would like to add that for me this thread was not in vain. I’ve learned quite a bit so for that I thank you all so much.

Myfriendis - I do what to show you that I took your request to heart so I’m including the support ticket info.

Strain: “One Pounder” can’t find the strain again, purchaed through ???
Method: Hydroponics
Vessels: 5 Gallon Bucket well cleaned, last rinse with H2O2 used with 2 aquarium air stones
PH: Water with nutrient, I try to keep it between 5.5 and 6.5 mpl adjusting daily as needed
EC of nutrient solution: using general hydroponics Flora series - 5.1
Grow Method: Indoor
Light system: Using LED but as pointed out that my “1000 watt” equivalent isn’t equivalent.
Temps: constant temp day/night, about 25c, I know that’s way too high and will correct that with better ventilation
Humidity: 65%
Ventilation: closed tent with 4" fan circulating air.
AC: none
Co2: Attempting unsuccessfully with yeast based generator.

Again thank you all


Don’t hurt to try the bags though, just sayin. :grinning:

I have a co2 bag right under this bw.

Under is a problem u want co2 to " rain down on your plant"