Carbon Dioxide Explained

This month we are looking at methods and the supplies and equipment needed for increasing CO2 levels in the grow room. Normal atmospheric CO2 levels are between 300 to 500ppm (parts per million), depending on whether you live in an urban or rural area. Increasing these levels to 1500ppm can often have dramatic effects on your plants, including faster growth rates and increased yields. This is why it is so important to always have fresh air circulating into your grow room. Or better yet, add supplemental CO2.

Carbon Dioxide Metabolism (in a scientific nut shell)

Many growers overlook the huge importance of CO2 to fast growing plants. CO2, along with light and water, are the three most important sources of food for plants. Nutrients are necessary for photosynthesis to occur, but they are mainly a catalyst to allow the reactions to take place. In fact, if you were to analyze any plant, you would find that it consists of over 90 percent water, a few percent nutrients, and the rest is carbon. Photosynthesis is the process by which plants use the energy from sunlight (or grow lights) to produce sugar, which cellular respiration converts into ATP, the "fuel" used by all living things. The conversion of unusable light energy into usable chemical energy is associated with the green pigment - chlorophyll. Most of the time, the photosynthetic process uses water and releases oxygen. We can write the overall reaction of this process as:

6H2O + 6CO2 + C6H12O6 + 6O2

Water enters the root system and is transported up to the leaves through the xylem. Plants have evolved specialized structures known as stomata to allow gas to enter and exit the leaf. Carbon dioxide cannot pass through the protective waxy layer covering the leaf, but it can enter the leaf through a stomata opening.

Light strikes chlorophyll in such a way as to excite electrons to a higher energy state. In a series of reactions, the energy is converted into ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate). Water is split in the process, releasing oxygen as a by-product of the reaction. The ATP and NADPH are used to make C-C bonds (carbon-carbon bond). During this process carbon dioxide is captured and modified by the addition of Hydrogen to form carbohydrates. The incorporation of carbon dioxide into organic compounds is known as carbon fixation. The energy for this comes from the first phase of the photosynthetic process.

The fixation or reduction of carbon dioxide is a process in which carbon dioxide combines with a five-carbon sugar to yield two molecules of a three-carbon compound. In the presence of ATP and NADPH the three carbon compound is reduced to triose phosphate. Most of the Triose produced is used to regenerate RuBP so the process can continue. The one out of six molecules of the triose phosphates not "recycled" often condense to form hexose phosphates, which ultimately yield sucrose, starch and cellulose. The sugars produced during carbon metabolism can be used for other metabolic reactions like the production of amino acids and lipids.

Methods of Increasing CO2 levels

There are many methods for adding CO2 to a grow room or greenhouse; however, not all are economical. Growers who have small grow rooms and don�t wish to purchase an expensive CO2 setup can always opt for the Excellofizz tablets. The Excellofizz tables are also perfectly suited to those growers who want to experiment with CO2. This method is cheap to setup but will cost more in the long run. Also, there is no way to control the output or maintain optimum CO2 levels in the grow room. Alternatively, you can use our CO2 Calculator to find the ideal system for your grow room.

Small Grow Rooms

- Excellofizz

Excellofizz is perfect for the grower who has been considering the use of CO2 but has been hesitating due to the high cost factor, or for growers in a small area. Try Excellofizz for 1 month during flowering and see what a difference CO2 makes.

Excellofizz is ideal for small indoor gardens. It allows for a simple and economical way of providing somewhat accurate CO2 to your plants with no equipment needed for dispensing or monitoring, especially in situations where venting is limited. Excellofizz emits the proper CO2 levels for indoor plants by reacting and giving off pure CO2 gas and also absorbing oxygen from the air. Simply place one of the Excellofizz pucks into the container provided. Pour 2-1/2 ounces of water into the container and leave the lid open slightly. Excellofizz will then slowly react, emitting the proper amount of CO2 gas for approximately 8 hours into the photo period. Excellofizz will then continue to increase CO2 levels after the reaction has completely subsided by absorbing oxygen from the air. Excellofizz is also fragrented with eucalyptus which is also known to repel mites and kill airborne bacteria.

Each puck, when reacted, will emit enough CO2 gas in a 10' x 12' area to raise the level by approximately 1600ppm. This will give a total of 1900-2200ppm for optimum growth. Many growers with smaller areas will break the pucks into two or more pieces to get more use out of the Excellofizz kit. Each Excellofizz Kit comes with 15 pucks.

Small to Medium Size Grow Rooms

Bottled CO2

Bottled CO2 is perfect for small areas up to around 12' x 12' x 8'. CO2 tanks are available in several different sizes, but the most common size used for enriching grow rooms is the 20lb tank. In addition to the CO2 tank, you will also need to purchase a CO2 Enrichment System to properly dispense the CO2. The enrichment system attaches directly to the CO2 tank with either a wrench or channel locks. Most enrichment systems consist of a pressure regulator and gauge, a solenoid valve, and a flow meter. The flow meter allows you to adjust the amount of CO2 coming out of the tank, and the solenoid valve allows you to attach a timer or other device to turn on and off the flow of CO2, thereby maintaining the desired level of CO2 (usually between 1500 and 2000ppm).

If you are using a CO2 tank with an Enrichment System there are two ways to determine the proper CO2 level and flow rate for your needs. The first is to use the BGH CO2 Calculator. The second is to do the calculations manually:

Determine the size of the room in cubic feet (CF). This is done by multiplying the length by the width by the height of your room. If your room measures 10’ long by 10’ wide by 8’ high, then your total CF is 10 x 10 x 8 = 800 CF.
Determine what your desired level of CO2 is and subtract the existing amount of CO2 that’s already present in your room. Most growers will prefer about 1500ppm (parts per million) of CO2. Plants will respond to up to 2000ppm, but this amount is generally not used since plants will utilize such high levels only if every other aspect is in perfect balance (which is extremely difficult to achieve). In general, there is about 500ppm of CO2 already present in the atmosphere if you live in a big city, around 300 if you’re in a less populated area. Assuming that there is 300ppm present where you live, you would have to add an additional 1200ppm in order to reach your target level of 1500ppm.
Determine how many CF of CO2 you need to inject. Multiply the volume of your room by the amount of CO2 necessary to raise the CO2 ppm to the target level: 800 CF x .0012 = 0.96. We will round 0.96 up to 1. Therefore, in order to raise the ppm level in your room to 1500ppm, you will need to inject 1 CF.
Determine the flow meter setting. Assuming that after 3 hours CO2 levels will return to normal due to plant use as well as leakage, we will divide the 1 CF of CO2 into three 1 hour increments. 1 CF divided by 3 = 1/3 CF or 0.333. Therefore, every hour an 800 CF room needs 1/3 CF of C02 in order to bring it back up to 1500ppm, and so your flow meter should be set to 0.333.

Medium to Large Grow Rooms

CO2 Generators
CO2 Generators are generally more expensive than CO2 tanks and also produce a small amount of heat, but they offer several advantages. Generators operate on either propane or natural gas, both of which are less expensive and easier to come by than bottled CO2. Propane generators can operate using just about any propane tank, including the small ones used for barbeque grills. Some growers use the natural gas hookup provided for a gas clothes dryer in their house to attach natural gas generator, which not only saves the labor of swapping out empty propane tanks, but also saves them money, as natural gas is much cheaper than propane. Some generators, such as the MegaGrowth, are vented so that you can attach an exhaust fan and eliminate some of the heat they produce. It is highly advisable to use a digital CO2 controller with a CO2 generator as it is fairly easy to go over 2000ppm of CO2 when using these burners. A digital CO2 controller will keep the CO2 levels within the optimum range and will not allow the generator to wander outside that range.

Calculating the size of a CO2 Generator

It is important that the correct CO2 Generator is purchased for a specific grow room size. If you purchase a generator that is too small then it would burn for to long and heat up the grow area excessively. There are two ways to determine the correct generator size for your needs. The first is to use the BGH CO2 Calculator. The second is to do the calculations manually:

Room Size – L x W x H = V eg: 12’ x 15’ x 8’ = 1440 cubic feet
CO2 Required – Volume of room (V) x CO2 ppm required eg: 1440 x 0.0012 = 1.7 cubic feet of CO2. The desired ppm of CO2 is 1500ppm however, we need to subtract the ppm of CO2 that is already in the atmosphere (normally 300ppm). This leaves us with an amount of 1200ppm (which equals 0.0012) that is required to be generated to raise the ppm in the grow room to 1500ppm.
Selecting a CO2 Generator. Each generator will have a CO2 output per hour. e.g. the Green Air CD-6 has a CO2 output of 6 cubic feet per hour.
Burn Time – 6 cubic feet / 60 min = 0.1 cubic feet per minute. Therefore to produce 1.7 cubic feet of CO2 the Burn Time will be 1.7 cubic feet of CO2 / 0.1 cubic feet per minute = 17 minutes Burn Time.

Ideally you want to keep the burn time short as possible, preferably less than 10 minutes, thus the CD-6 burner will be to small for that size room. A CD-12 burner would have been a better choice, the burn time would be about 8 minutes.

- PnG Smart CO2 Generator

The Plug 'n' Grow Smart CO2 Generators are safe, easy to use and extremely efficient. With their electronic pilot, they are safer and more economical than burners with a pilot flame that is constantly burning. Also, all models have an internal electronic high temperature cut-off switch to avoid excessive heating and increased safety (which can be a real crop saver). Models with heat exchangers will also help keep grow room temperatures cooler. In fact, just connect the exchanger to an intake and exhaust vent hole with flexible ducting to exhaust the excess heat outside or to another room for heating. This way only heat is vented outside the grow room without affecting the CO2 or the humidity levels.

PnG Smart CO2 Generator - 4 Burner (LP) - 15 cubic feet/hr - 12 000 btu
PnG Smart CO2 Generator - 8 Burner (LP) - 29 cubic feet/hr - 24 000 btu

- Green Air CO2 Generators
Carbon dioxide generators operate by burning carbonaceous fuels such as propane or natural gas. The burners used in Green Air Products CO2 generators are specially designed to maximize the production of CO2 and minimize heat as a by-product. A constant burning pilot is used to ignite the gas when the generator is turned on. A thermocouple is used to monitor the pilot flame. If the pilot flame is lost, a safety valve will close so that unburned fuel will not be released into the growing area. Generators are easily installed, dependable and efficient. Operates on 110 VAC. NOTE: LP denotes propane model; NG denotes natural gas model. Please choose the correct model when placing your order.

CD-3 – LP and NG – 3 cubic feet CO2 per hour
CD-6 – LP and NG - 6 cubic feet CO2 per hour
CD-12 – LP and NG - 12 cubic feet CO2 per hour
CD-18 – LP and NG - 18 cubic feet CO2 per hour
CD-36 – LP and NG – 36 cubic feet CO2 per hour

- MegaGrowth Burners
MegaGrowth CO2 Generators were developed through intensive research and development and over nine years of testing to produce a highly effective carbon dioxide generator. Their innovative design is vented at the top so the heat can be disposed of without losing any carbon dioxide. The innovative solid brass impinged burners allow a consistent clean burning blue flame. Their crafted, top of the line gas valves use the most modern method igniter in the industry. No need for a gas pilot light thus no added heat, no gas wasted, no pilot light to go out. Easy to light - when you light the first, the others automatically light up. MegaGrowth generators are available in 4, 6, 8, and 18 burner sizes.

"LP" denotes propane and "NG" denotes natural gas. Propane generators require a propane tank of any size (the ones used for barbeques will work just fine), all fittings and tubing are included. The Natural Gas models are designed be hooked up to a natural gas line (existing gas lines for clothes dryers are perfect), and they already include the necessary regulator and tubing.

MegaGrowth 4 Burner (LP) - (NG) - 15 cubic feet/hr - 12 000 btu
MegaGrowth 6 Burner (LP) - (NG) - 22 cubic feet/hr - 18 000 btu
MegaGrowth 8 Burner (LP) - (NG) - 29 cubic feet/hr - 24 000 btu
MegaGrowth 18 Burner (LP) - (NG)- 65 cubic feet/hr - 50 000 btu

The most accurate and efficient method of controlling CO2 concentration in a grow room is with the use of a digital CO2 controller or “sniffer”. These digital “sniffers” use an infrared sensor to detect the level of CO2 in the grow room. The CO2 controller should never be placed next to the burner; ideally it should be placed on the opposite side of the grow room at canopy level. The CO2 burners can hang from the roof (not to close to the ceiling though) or be placed on the floor. Place an oscillating fan in front of the burner; this will help disperse the CO2 evenly in the room. The fan will also keep the air mixed and stop the CO2 from settling near the floor (be careful not to place the fan too close to a Green Air CO2 Generator as it may blow out the pilot light).

IGS 61
This digital controller performs CO2 enrichment or venting using an integrated infrared 0-5000ppm CO2 sensor. A high temperature shut-off feature inhibits CO2 enrichment if the temperature in the grow room exceeds the value set by the grower. This controller uses proprietary PnG CO2 control algorithms which enable the controller to adapt to any size or type grow room/greenhouse. The large digital display constantly provides a read out of the CO2 level in the room.

The IGS 61 will only enrich CO2 during the day (when light is sensed by the photocell). The enrichment starts when the CO2 concentration falls below the set point minus the differential (which is user-definable). i.e. set point = 1500 ppm Differential = 150, CO2 enrichment will start once the CO2 level falls below 1350 ppm and stops beyond the set point plus the differential eg. 1650ppm. The differential modifies itself until the controller senses no more overshooting or undershooting of the user set point. Fixed differential values can also be set for more specific needs. As a safety feature, the high temperature shut off function will inhibit operation while temperature is over the user setting. This interruption is maintained until the temperature falls below the user high temp setting. This feature is great for growers using CO2 generators. All generators produce some amount of heat, and if your cooling system ever malfunctions it's great to know that your generator won't turn on and make things even hotter. To inhibit this feature, simply set the limit to its highest value. The controller can also be set to ventilate the grow room, also extracting the CO2 from the room. In this case, the high temp shut off feature becomes a low temp shut off limit to prevent excessive cooling conditions.
IGS 220
The IGS 220 CO2, relative humidity and temperature controller is the simplest and most complete solution to integrated climate management and CO2 enrichment or venting. The resulting climate can increase yields and quality of harvest while insuring CO2 and energy savings. The device displays the actual values of CO2, relative humidity and temperature sensors. The controller includes an internal fan to speed up the air sampling process, thus yielding a more accurate climate control. The control unit can be positioned up to 6 feet away from the output box (a standard CAT-5 data cable up to 50 feet can be used). The control unit logs the last 24 hours minimum, maximum and average CO2 concentration, relative humidity and temperature values. Multiple operation modes are available and the differential of operation is adjustable.

The IGS 220 has multiple configurations which enables the user to prioritize CO2 control over temperature or relative humidity management or vice versa. Optional timers (5 and 10 minutes) can be set to maintain the output OFF after CO2 enrichment process has ended.

The IGS 220 also constantly analyzes its performance and issues (in the form of hint codes) a report to the user. The percentage ratio of the ON time of each output is obtainable through the hint codes. The 24 hour datalogger lets the user follow-up on the evolution of CO2 concentrations, relative humidity and temperature, day and night. The IGS 220 can also activate a dry-contact output when temperature or RH values go outside user limits or when a power outage has happened. This dry-contact output can be connected to a back-up system, an alarm system or an automatic dialer.

After a full year of use the IGS 220 will display an error message which indicates to the user that a recalibration of the CO2 sensor is advised. Once the procedure is performed (10 minutes maximum) this message will disappear to reappear a year later. The controller also offers an altitude correction factor (up to 9500 feet).
CO2 Detector Kit
This inexpensive CO2 test kit is ideal for small grow rooms, especially if Excellofizz tablets are being used. It's also a great tool for double-checking your CO2 calculations to make sure your system is really putting out the amount of CO2 you think it is. This kit gives a fairly accurate reading, is easy to use and is cheap. This kit includes one 100cc syringe, two CO2 test tubes and instructions. Simply hold your breath and draw in 100 cc's of the room's air into the syringe. Next, break the ends off a tube and insert the tube into the syringe. Then, slowly force the air through the tube; it should take 1 minute to push the air through the tube. The number where the purple color stops and the white begins is the CO2 concentration inside the growing area.
MCC-1
The Micro Climate Controller MCC-1 is designed to perform all the major atmospheric and timed functions required in an automated growth environment including temperature, humidity, carbon dioxide enrichment, lighting and irrigation control. CO2 equipment can be operated from the CDDS-1 trigger when using the CDMC-2 infrared monitor controller. This outlet provides an exhaust synchronized override feature to delay enrichment during ventilation periods. When timed control is desired plug CO2 equipment into CO2 outlet and set timer mode toggle switch accordingly. Set the sequence timer duration dial for minutes of ''On'' time and frequency dial for the time between ''On'' functions. Exhaust demand will override CO2 production and timer will reset to cycle immediately following ventilation. CO2 outlet is defeated by a built-in photo sensor to operate only when light is present. The MCC-1 controller also incorporates an external coil cooling thermostat , a dehumidifying humidistat, a 24-hour clock timer, a photo-sensor and a repeat cycle timer. Heating and humidifying control is provided by triggers for remote high-amperage relays which enable synchronized equipment management. Automatic override and defeat systems coordinate controls to consider all possible variables. The MCC-1 is enclosed in a black anodized, brush finish aluminum housing. An attractive screen-printed front panel with function indicator lights makes system monitoring and adjustment quick and easy. All connections are standard 3-prong grounded plugs and receptacles. No hard wiring is required for basic operations. Low and high voltage relays are available to operate auxiliary equipment. Every aspect of the growing environment may be addressed by the Micro Climate Controller (MCC-1). Operates on 110VAC with 15 Amp switching capacity. The MCC-1 was designed to be used independently or in conjunction with Green Air Products function relays. The MCC-1 will serve independently for systems and equipment requiring 110 VAC of 15 Amps or less. Plug power cord into standard wall outlet and locate controller where good air circulation represents plant zone conditions. Plug exhaust fan into exhaust outlet. Set thermostat and humidistat dials to maximum desired values. Fan will operate when conditions exceed those set points. Function indicator lights will display the condition and outlet status. The 24 hour clock timer is useful for all daily oriented timing operations. The 96 independent 15 min trippers allow any combination of on/off functions repeated each 24 hours. Lighting, fans, pumps and watering are only a few of the tasks this timer can perform. If your combined amperage draw exceeds 15 amp power handling capacity of the controller optional high amperage function relays can be used to provide service to large systems.
CT-DH 3 & CT-DH 3P
Specially designed to coordinate CO2 enrichment with ventilation. Plug exhaust fans into the right side outlets, CO2 into the left side outlets. Set the dials on the CT-DH-3 to the desired temperature and humidity. Now sit back and relax. If the the temperature or humidity gets too high, the CO2 side will turn off and the the fan side will turn on. Once the temperature and humidity fall back to within the proper range, the fans will shut off and the CO2 side will turn back on again. BGH recommends plugging an IGS-11 (or IGS-11) into the CO2 side of the CT-DH-3 and then plugging your CO2 equipment into the IGS-11. That way, when the power is restored to the CO2, the IGS-11 will automatically reset itself, dispense CO2 for the proper length of time, and then shut off until the next release of CO2 is needed. (You can't do this with a regular 24 hour timer because every time the power is cut off from the CO2 side, the time will become incorrect on the timer, and then your CO2 won't dispense properly).

The CT-DH 3P model is equipped with a built-in photo sensor to defeat the CO2 outlet during the dark period. However, both the IGS-10 and IGS-11 also have built-in photo sensors so there is no need to spend the extra money on the "P" model. Neither the CT-DH 3 nor the CT-DH 3P use infra-red CO2 “sniffers” to monitor the CO2 in a grow room. These two units give a timed release of CO2. If you are using bottled CO2 then you will still require the CO2 Regulator Kit that connects to the CO2 tank. The solenoid will plug into the CT-DH 3 or CT-DH 3P for automation.
CDMC-6
The CDMC-6 package includes the CDDS-2 Controller and the CDM-6001 Monitor. The Green Air Products CDM-6 CO2 monitor is a breakthrough in CO2 detection and control. It is a sensing device which measures the level of CO2 in the air. It employs a revolutionary passive infrared element which samples the air once every second and interprets a value instantly. This enables you to maintain precise CO2 enrichment levels without guesswork. The monitor plugs directly into Green Air Products Carbon Dioxide Digital Sequencer (CDDS-2), which enables the user to adjust the desired CO2 level and span. All you do is plug the CO2 Monitor and your CO2 generator or bottled CO2 Enrichment System into the CDDS-2, set the values you want, and it will maintain your desired CO2 level perfectly and constantly all day. CO2 values are adjustable in 10 ppm increments from 0 to 5000 ppm. The span between CO2 "on" and CO2 "off" is also adjustable in 10 ppm steps up to 300 ppm differential. The LED changes color to indicate CO2 function status. The CDDS-2 also provides a switchable photo sensor to disable CO2 production during periods of darkness.
CDMC-7
The CDMC-7 package includes the CDDS-2 Controller and the CDM-7001 Monitor. The Green Air Products CDM-7001 CO2 monitor is a breakthrough in CO2 detection and control. It is a sensing device which measures the level of CO2 in the air. It employs a revolutionary passive infrared element which samples the air once every second and interprets a value instantly. The passive infrared sensor precisely determines and displays the CO2 values in parts per million (ppm) on a large LCD screen. This enables you to maintain precise CO2 enrichment levels without guesswork. The monitor plugs directly into Green Air Products Carbon Dioxide Digital Sequencer (CDDS-2), which enables the user to adjust the desired CO2 level and span. All you do is plug the CO2 Monitor and your CO2 generator or bottled CO2 Enrichment System into the CDDS-2, set the values you want, and it will maintain your desired CO2 level perfectly and constantly all day. CO2 values are adjustable in 10 ppm increments from 0 to 5000 ppm. The span between CO2 "on" and CO2 "off"is also adjustable in 10 ppm steps up to 300 ppm differential. The LED changes color to indicate CO2 function status. The CDDS-2 also provides a switchable photo sensor to disable CO2 production during periods of darkness. The CDM-6 sacrifices the digital display and portability for a more economical price (you still have the digital readout on the CDDS-2 controller, so you will still be able to see the ppm of CO2 in the room).
SPC-1
This new, easy to install and operate CO2 enrichment controller is factory calibrated and inspected for optimum performance. The SPC-1 is designed with a photo sensor to defeat CO2 enrichment during dark periods with a large easy to read real-time LED display. The SPC-1 is also programmed with a preset differential (hysteresis) of 20 PPM and offers an elevation adjustment feature to fine tune performance. Operated on 120 Volts AC with 12 Amps switching capacity.