Revisiting problem of rising CO2 at night

[Warrioreuel]

Small update. I checked the room at 7 this morning. Door has been open a foot for a week now with a small floor fan. Finally for the first time the CO2 level was 375. I thought oh good what ever was going on has finally subsided. I closed the door and 4 hours later the CO2 was 1050 ppm. I am leaning towards the concrete either off gasing or something under it is generating CO2. Here is another perhaps important piece that i just realized could be a factor. I like to keep my young plants at a humidity of 70% or so. The humidifier I have used in the past just makes a huge mess when you use it, spits water every where making it hard to locate it knowing it will soak the walls and any other equipment near it. So as a stop gap measure i watered down the bare concrete floor with my regular 160ppm tap water. This works wonderfully at keeping the humidity up and its a cheap and easy fix to raise humidity. I have not done this now in a week or so since i realized my CO2 levels were so sky high. So i don't know but maybe the concrete gives off CO2 when its wet. I know it absorbs water like a sponge. Too hard to cover the floor in plastic at this point with the system all setup. However, when the room is empty again I will paint the floor to try and seal it. CO2 absorbent will be here this week. Will filter all incoming air through that before bubbling it through the water and see if this helps. Leaving the door open and lowering the CO2 levels has helped tremendously but still they suffered the initial damage and are now off to a really slow start. Thinking back i never had this problem when i had seedlings just in a garage with a 40 years old concrete floor. Again i am suspecting the new concrete or something under it off gassing. This room is 10x20 with 12 foot ceilings so the CO2 rising from 375 to 1050 in 4 hours is substantial. If after trying the absorbent to filter the air fails to lower the level then I will drain the whole thing, disassemble it and put down plastic. I prefer paint but don't want to risk fumes at this point. Side note, I keep water temps at 65-66 degrees.

 

[Aqua Man]

Possible it's a chemical reaction to your water but tap water is usually alkaline not acidic so that makes me wonder. It's very possible that under the concrete something is creating large amounts of CO2 and the concrete is absorbing it from one side and off gassing on the other? I don't know how fast this permeation would happen but just a thought.

 

[Deadstill]

Ok. Now it all makes sense. The co2 is definitely coming through the concrete. The reason it's coming out at night is directly related to the lights being off. The increase in temperature from the lights is essentially "opening the pores" of the concrete making it swell and absorb co2. When the lights go off and it cools, the concrete shrinks and forces the co2 out. Then you said you were adding water. This is just like the soil capping I mentioned. Water comes in, the gas inside has to come out. This is probably coming from your soil (being a heavily wooded area I'm sure the soil is high in nutrients). Seal the floor I bet you 20 bucks the problem goes away or at the least will make a drastic difference.

Also the concrete is likely more porous since it's new, which is why you didn't have this problem with old concrete that was likely saturated with oils and gunk over 40 years.

 

[Warrioreuel]

Yes, the new concrete is looking more and more like the culprit. And yes, the concrete even though finished nice and smooth it seems very porous to water. I guess i could water it down and verify one last time the CO2 level shoots up. Long term fix, painting is in order. Short term i reluctantly will dismantle the equipment and put down plastic. It will take a week or two before i have (no pun intended) any concrete results but, i will let you guys know the verdict. In the mean time I still want to test removing CO2 from the air since i have the absorbent material on its way. Wonder how long the concrete would naturally stop off gassing or sinking CO2? If its porous, maybe never? Or maybe several years making it impractical to wait it out.

 

[Jimster]

Yes, the new concrete is looking more and more like the culprit. And yes, the concrete even though finished nice and smooth it seems very porous to water. I guess i could water it down and verify one last time the CO2 level shoots up. Long term fix, painting is in order. Short term i reluctantly will dismantle the equipment and put down plastic. It will take a week or two before i have (no pun intended) any concrete results but, i will let you guys know the verdict. In the mean time I still want to test removing CO2 from the air since i have the absorbent material on its way. Wonder how long the concrete would naturally stop off gassing or sinking CO2? If its porous, maybe never? Or maybe several years making it impractical to wait it out.

Any time the water is slightly acidic, it will cause concrete or cement to offgas, especially newer cement that takes a few years to fully cure. Salt will do the same as it dissolves cement slowly, as evidenced by sidewalk damage that happens when salt is applied, engraving the surface. A simple CO2 removal system that is dirt cheap to use is simply an air pump and a large 5-6 gallon or larger container, filled with water. Add a bunch of Calcium Hydroxide to the water. The water should turn clear. Pump the CO2 laden air thru the Alkaline water, and the CO2 will precipitate out as Calcium Carbonate, which is insoluble in an alkaline solution. The solution needs to be recharged every so often, but Calcium Hydroxide is pretty cheap and known as Caustic or pickling lime. The final product, known as Limewater, causes CO2 to precipitate out of the air when pumped thru it.

 

[Comermac]

In his book Ed Rosenthal mentions that at night plants release co2. This is why he recommends not adding co2 with an external system for the first hour or two of the lighter being on.

Edit: my 2 cents is that as long as it goes down during the day you are good. If the lights arent on the plants are not performing photosynthesis therefore not taking in co2.

 

[Aqua Man]

In his book Ed Rosenthal mentions that at night plants release co2. This is why he recommends not adding co2 with an external system for the first hour or two of the lighter being on.

Edit: my 2 cents is that as long as it goes down during the day you are good. If the lights arent on the plants are not performing photosynthesis therefore not taking in co2.

But they are respiring

In his book Ed Rosenthal mentions that at night plants release co2. This is why he recommends not adding co2 with an external system for the first hour or two of the lighter being on.

Edit: my 2 cents is that as long as it goes down during the day you are good. If the lights arent on the plants are not performing photosynthesis therefore not taking in co2.

Now that you mention it I think the problem was the opposite of what I thought and that makes more sense. With my timer starting and stopping that would mean during the day period I would have no CO2 at times and that was more likely the problem rather than the high night times. Those symptoms fit the bill. Here I thought it was the night time levels that caused it because that when I noticed. I kinda feel foolish now.

 

[Aqua Man]

Oops posted in the wrong thread. Meant to post in my thread about high ppm CO2 at night. Where I plugged my timer in the controller instead of the other way around.

Sorry carry on

 

[Warrioreuel]

I see a lot of ideas here to try to lower my CO2. If the plants were already 2 feet tall or so then this would not be a problem as any CO2 off gassing from the floor would be a welcome freebee as the plants would use every bit of it and lessen the load for me adding extra during the day with a tank. It is only when they are small and the CO2 builds up in the room that it is a problem. I got me CO2 absorbent media today so in the next day or two I will see if that makes any difference. Depending on the results of that little experiment I may try bubbling the room air through a Calcium Hydroxide solution and compare results. Long term I will also see how practical it is to put plants in the room that consume CO2 even at night. One such plant is an Areca Palm. You see them standing in the corners of the lobby at places like restaurants. If you search the internet you can find lists of such plants.

 

[Comermac]

Have you seen any negative side effects or just the high number?

 

[Warrioreuel]

I would not be concerned at all about higher CO2 accept the 3000 ppm CO2 level just about killed the seedlings. I have spent the last 10 days getting the levels down and now finally they are for sure recovering. Not sure if the long term affect will be a stunted plant like a early root rot problem. I know from experience that even curing root rot on young plants that the final adult always seems stunted, small and turns out to be an under performer. I am hoping these seedlings develope into healthy adults. Right now I am hopefull as the roots look great and the leaves are looking healthey again with new growth start. They are still only 3 or 4 inches tall but recovering.
You might ask how I am so sure this is CO2 poisoning. I have been growing for years now and have seen about everything go wrong that can go wrong. This is the third crop in this new room. Both the previous two crops had the exact same problem but i never identified the CO2 being so high (as I never thought to look) when they were so young. I poisoned some planted a few years ago when i experimented with intentionally raising the CO2 level to 5000 ppm to try and kill mites. Side not, don't bother doing that, it is a waste of time and will injure your plants.

 

[Comermac]

I am interested to hear if the co2 absorbent works out for you. What are symptoms of co2 poisoning? I am installing a sensor and co2 regulator in my grow. I will definitely be looking at the nightly number. I wonder if the co2 in my tents will raise that much.

You mentioned a timer so I'm guessing you have a tank and regulator right?

 

[Aqua Man]

I am interested to hear if the co2 absorbent works out for you. What are symptoms of co2 poisoning? I am installing a sensor and co2 regulator in my grow. I will definitely be looking at the nightly number. I wonder if the co2 in my tents will raise that much.

You mentioned a timer so I'm guessing you have a tank and regulator right?

I use a timer and controller but most controllers have a light sensor. I would make sure to run a controller for the simple reason if wasting CO2. Also you really only need to run it beginning of flower until about 2-3 weeks before harvest unless you are supplementing at which point 500-600 ppm is more than enough for the rest of the time.

 

[jumpincactus]

Thank you for all replies. This is a metal building I had built. Poured the concrete slab 1 year ago to date. There is no controller or CO2 tank in the room at all, i removed it until i figure out what is going on here. It has 12 seedlings a few inches tall. However, there is 120 gallons of water circulating in a DWC setup with Cal-Mag, Aqua Flakes and nitric acid to keep the PH just under 6. It also get about 150 ml of UC roots once a week to keep away root rot. Since the seedlings are small my nutriet strength right runs approx 120 ppm. This is not my first setup but it is a new grow room in a new area so to speak. The RO water by itself is almost exactly PH 7 with 20 ppm, so its pretty clean. At this point my list of suspects (process eliminatus) is the concrete is off gassing CO2 (or poured on top of a CO2 source bubbline through the floor), the OSB walls, the paint and now possibly the nutrients in the water off gassing (had not thought of that before). So far i have left the door open now for a week with a floor fan and the levels are down to low 400's. If I close the door they will rise so as a stop gap measure i will simply leave the door open for now. CO2 absorbent media hopefully be here this week. When it gets here my intention is to route the air through it before it bubbles through the air stone. I am hoping that this will least scrub my water of CO2 which was most likely saturated with CO2 gas when the room was 3000 ppm. It would be nice to have a device to check to dissolved CO2 level in the water to see if I am actually having any impact with my corrective measures. I suppose recovered healthy plants will be the final indicator but I like to know really what is going on. I suppose if this were a dirt grow then the free CO2 would be fine. But, in hydro it is poisoning my water.
Here are some questions. Is an OSB walled painted with latex a true barrier for CO2 or does it pass through the wall as if it were nothing more than a bug screen? Does concrete retain CO2 like a sponge? In other words when my levels were over 3000 ppm, did the concrete absorb this and now slowly releasing it?

Concrete does capture co2 by a process called carbonation.

"A significant portion of the CO2 produced during manufacturing of cement is reabsorbed into concrete during the product life cycle through a process called carbonation. One research study estimates that between 33% and 57% of the CO2 emitted from calcination will be reabsorbed through carbonation of concrete surfaces over a 100-year life cycle."

Understanding Carbonation

Read how carbonation poses a threat to concrete's durability, strength and ultimately, safety of precast concrete products.

precast.org

 

[Jimster]

I poisoned some planted a few years ago when i experimented with intentionally raising the CO2 level to 5000 ppm to try and kill mites. Side not, don't bother doing that, it is a waste of time and will injure your plants.

Bugs aren't bothered too much by high CO2 levels... they just sort of fall asleep and wake up as soon as the air is OK again. I had some bugs in a somewhat similar situation where I couldn't use any type of spray and the CO2 looked like a good idea. Dutifully, the bugs all fell over after the CO2 introduction and stayed that way for a few hours. As soon as I vented the stuff out, they yawned, rolled over, asked what time it was and got back to their destructive business. I thought cockroaches were hard to kill... Mites are so small that you don't even know you have them until the damage shows up... cockroaches are big enough to see and stomp on.

 

[jumpincactus]

@Jimster is on to something, I am also agreed with those of you that think the newly poured concrete slab is the culprit.

Some concrete mixes can take years to stop curing. OP says his slab is only a year old.

Digging deeper into the curing process, hydration is the chemical process that allows concrete to go from a plastic state to a hardened state while gaining strength over time. Hydration occurs at a faster rate in the early stages after concrete placement and slows down after a month or so goes by. Many cement pastes will cease hydration before one year, and some may continue to hydrate over the course of several years (4). Because of the variable length of the hydration process, the phrase “green concrete” is a purely subjective characterization.

It would also be interesting to know what the chemical composure of the lot/soil is under the slab. Even when concrete is fully cured it remains slightly porous. My theory is something under the slab, maybe vegetation going thru decomposition allowing it to rise thru the capillary matrix in the slab raising C02 levels. Along with the fact the slab is still so new.

 

[Warrioreuel]

Little more side info while I am waiting on CO2 level results.Yes, i use tank CO2 with a standard little solenoid valve controlled by an Autopilot APCECOD CO2 controller. It turns itself off at night and works perfect. Key to getting good results - adjust your release rate on the tank regulator so the little green ball in the sight window is super slow. For the first year or so i thought this controller was a real waste of money. Turns out i was using is it wrong or more precisely had the release rate of the CO2 way way way too fast. Once you understand how this thing works it will make more sense to set the release rate to a real slow rate. This gives the CO2 time to disperse and equalize in the room rather than the blasting it out at full speed which drives the sensor crazy. As I mentioned before, right now the entire CO2 system controller and tank is completely removed from the room. Not able to test the media yet as one part did not come in yet. I could just pour it in a bowl, close the door and see how it does. But. what i want to do is actually run the air through the media just before bubbling it into my water. If the air bubbling through the water is void of CO2 this should help cleanse the water of any excess if there is any. Without being able to measure dissolved CO2 in water I am assuming that when i was bubbling 3000 ppm levels that the water could be CO2 laden. How fast the water releases this to the surrounding air i can only guess. The door to the room is still open, floor fan running. Todays level was 420, still higher than normal air. My meter works fine, took it outside in open space and it checked in at 379 ppm.

 

[Aqua Man]

Little more side info while I am waiting on CO2 level results.Yes, i use tank CO2 with a standard little solenoid valve controlled by an Autopilot APCECOD CO2 controller. It turns itself off at night and works perfect. Key to getting good results - adjust your release rate on the tank regulator so the little green ball in the sight window is super slow. For the first year or so i thought this controller was a real waste of money. Turns out i was using is it wrong or more precisely had the release rate of the CO2 way way way too fast. Once you understand how this thing works it will make more sense to set the release rate to a real slow rate. This gives the CO2 time to disperse and equalize in the room rather than the blasting it out at full speed which drives the sensor crazy. As I mentioned before, right now the entire CO2 system controller and tank is completely removed from the room. Not able to test the media yet as one part did not come in yet. I could just pour it in a bowl, close the door and see how it does. But. what i want to do is actually run the air through the media just before bubbling it into my water. If the air bubbling through the water is void of CO2 this should help cleanse the water of any excess if there is any. Without being able to measure dissolved CO2 in water I am assuming that when i was bubbling 3000 ppm levels that the water could be CO2 laden. How fast the water releases this to the surrounding air i can only guess. The door to the room is still open, floor fan running. Todays level was 420, still higher than normal air. My meter works fine, took it outside in open space and it checked in at 379 ppm.

Yup I set mine to reach max ppm in an hour when the room is empty of plants. Allows for dispersal and equalization of CO2 so you don't get that creep after it shuts off

 

[Comermac]

I use a timer and controller but most controllers have a light sensor. I would make sure to run a controller for the simple reason if wasting CO2. Also you really only need to run it beginning of flower until about 2-3 weeks before harvest unless you are supplementing at which point 500-600 ppm is more than enough for the rest of the time.

I use a timer and controller but most controllers have a light sensor. I would make sure to run a controller for the simple reason if wasting CO2. Also you really only need to run it beginning of flower until about 2-3 weeks before harvest unless you are supplementing at which point 500-600 ppm is more than enough for the rest of the time.

My setup is controlled with a raspberrypi so I am able to skip the light sensor. I can check that with code.

 

[Warrioreuel]

Digging deeper into the curing process, hydration is the chemical process that allows concrete to go from a plastic state to a hardened state while gaining strength over time. Hydration occurs at a faster rate in the early stages after concrete placement and slows down after a month or so goes by. Many cement pastes will cease hydration before one year, and some may continue to hydrate over the course of several years (4). Because of the variable length of the hydration process, the phrase “green concrete” is a purely subjective characterization.

It would also be interesting to know what the chemical composure of the lot/soil is under the slab. Even when concrete is fully cured it remains slightly porous. My theory is something under the slab, maybe vegetation going thru decomposition allowing it to rise thru the capillary matrix in the slab raising C02 levels. Along with the fact the slab is still so new.

As far as the concrete is concerned, i was there when it was poured. Like code dictates there was heavy plastic put down first. However the plastic is in 10 foot wide pieces so I guess its not sealed at all on the overlapping seams . I assume a gas like CO2 will find the seams. For all i know the plastic is permeiable to CO2 as well, i just don't know. I do know that just becasue its plastic and you think it would be a barrier does not mean it is. Some gases go right through certain materials. I am still on the fence as to whether or not the CO2 is coming from the concrete or off gassing from the water after i add nutrients. Maybe its both as I can not seem to get definitive results either way. Soon as I am able I am going to seal the floor with some sort of sealer. Doing research to verify that a particular sealer will in fact stop CO2. I am not assuming just any old sealer will or will not work. Still opening the door most days to release CO2 as it builds.