Marijuana Horticulture: The Indoor/Outdoor Medical Grower's Bible

ground of a rain forest covered with decaying organic matter could be two to three times as high as normal, but bringing a compost pile inside to cook down is not practical. Dry ice is made from frozen CO 2 . The CO 2 is released when dry ice comes in contact with the atmosphere. It can get expensive and be a lot of trouble to keep a large room constantly supplied with dry ice. It is difficult to calculate how much CO 2 is released into the air by fermentation, decomposition, or dry ice without purchasing expensive equipment.
CO 2 Emitter Systems
    Compressed CO 2 systems are virtually risk-free, producing no toxic gases, heat, or water. These systems are also precise, metering an exact amount of CO 2 into the room. Carbon dioxide is metered out of a cylinder of the compressed gas using a regulator, flow meter, a solenoid valve, and a short-range timer. Two types of systems are: continuous flow and short range. Metal carbon dioxide cylinders which hold the gas under 1000 to 2200 pounds of pressure per square inch (psi) (depending upon temperature) can be purchased from welding or beverage supply stores. The cylinders are often available at hydroponic stores. In North America, cylinders come in three sizes: 20, 35, and 50 pounds (9, 16, and 23 kg), and average between $100 and $200 (with refills costing about $30). Tanks must be inspected annually and registered with a nationwide safety agency. Welding suppliers and beverage suppliers often require identification such as a driver’s license. Most suppliers exchange tanks and refill them. Fire extinguisher companies and beverage supply companies normally fill CO 2 tanks on the spot. If you purchase a lighter and stronger aluminum tank, make sure to request an aluminum tank exchange. Remember, the tank you buy is not necessarily the one you keep. To experiment before purchasing equipment, rent a 50-pound (23 kg) tank. A large 50-pound (23 kg) cylinder is heavier but saves you the time of returning to the store to have it refilled. When full, a 50-pound steel tank weighs 170 pounds (77 kg). A full 20-pound (9 kg) steel tank weighs 70 pounds (32 kg) and might be too heavy to carry up and down stairs. A full 20-pound (9 kg) aluminum tank weighs about 50 pounds (23 kg), and a full 35-pound (16 kg) tank weights 75 pounds (34 kg). Make sure CO 2 tanks have a protective collar on top to shield the valve. If the valve is knocked off by an accidental fall, there is enough pressure to send the top (regulator, flow meter, valve, etc.) straight through a parked car.

When open, the red on/off valve on top supplies compressed CO 2 via the regulator and flow meter. An electric solenoid valve controls the timed bursts of CO 2 gas.
    Buying a complete CO 2 emitter system at a hydroponic store is the best option for most closet growers. These systems offer a good value for small indoor growers. You can make your own system as described below, but these systems often cost more than the pre-manufactured models.

A setup consists of a tank of CO 2 gas, regulator, solenoid valve, and a flow meter.
    Welding suppliers also carry regulators, and flow meters. Flow meters reduce and control the cubic feet per hour (cfh). The regulator controls the psi. Models with smaller flow rates, 10 to 60 cfh, are preferable for gardening purposes. Buy a quality regulator-flow meter. Buy all components at the same time, and make sure they are compatible.
    Carbon dioxide is very cold when released from a bottle where it has been kept under pressure. Even a quick blast can do damage to skin or eyes. If the flow rate is above 20 cfh, your regulator might freeze.
    A regulator and flow valve are essential, but the solenoid valve and the timer are optional. However, growers who do not use a solenoid valve and timer waste CO 2 . The solenoid valve and timer regulate the flow of CO 2 . A solenoid valve is electrically operated and is used to start and stop the gas flow from the regulator and flow meter. The least expensive timer is plastic and is commonly used for automatic sprinkler systems, but 240-, 115-, 24- and 12-volt systems are available. They cost about the same, but the lower voltages offer added safety from electrical shock.
    To automate the system, you need a “short range” digital timer to open the solenoid valve for brief periods several times a day.
    Control the exact amount of CO 2 released into the garden room by altering the flow and duration of CO 2 . To determine how long the valve should