Carbon Dioxide Explained

In this article 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. 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 6 burner will be to small for that size room. A 12 burner would have been a better choice, the burn time would be about 8 minutes.