Carbon Dioxide (CO2) is fundamental to the function and success of the planted aquarium. Carbon dioxide is a chemical compound composed of two oxygen atoms bonded to a single carbon atom (O=C=O).

During photosynthesis, terrestrial and aquatic plants use carbon dioxide and water, removed from the atmosphere and combined with light energy to produce oxygen and sugars. Free oxygen is released as a gas from the decomposition of water molecules (H2O), while the hydrogen is used to generate chemical energy required for the formation of sugars, or glucose. These sugars may then be consumed in respiration or used to produce polysaccharides, complex carbohydrates, such as starch, cellulose, proteins, and other organic compounds required for plant growth and development.

In the planted aquarium ecosystem, carbon dioxide is introduced through the use of a regulator in combination with other specialized CO2 equipment; a complete CO2 system designed to promote an ideal and balanced ecosystem.

To understand the regulator, we must first take a closer look at the CO2 Cylinder.

CO2 Cylinder – Carbon dioxide (CO2) in a cylinder exists primarily in the form of liquid CO2, only the head space of the tank contains gas. The liquid allows the cylinder to maintain a constant and high pressure; as long as the cylinder contains any amount of the liquid CO2 the regulator’s high pressure gauge will read full, between 800 – 1000 PSI. When the liquid has completely evaporated, CO2 remains in the tank in its gaseous state, and the pressure will decline to zero. Because the cylinder contains liquid gas, it must always remain in the upright position.

CO2 Pressure Regulator – designed to reduce the high pressure inside of a CO2 cylinder to a lower, usable pressure that can be dispensed. The pressure-reducing regulator takes a pressure of 800-1000 PSI (pounds per square inch) from the cylinder, and regulates it, providing a controlled, reduced pressure output in the range of 1-30 PSI. All CO2 regulators have CGA (Compressed Gas Association) 320 fittings for USA and Canada. A CGA 320 fitting has a 0.825-14 NGO-Right Hand Thread. It is recommended to invest in a regulator that is UL listed. A UL listed regulator has been tested and certified by the “Underwriters Laboratory”, a trusted source across the globe for product compliance, to meet their safety requirements.

High Pressure Gauge – located at the nine o’clock position, it reads the amount of pressure present in the cylinder. As long as there is liquid gas in the cylinder the pressure will read at or around 800 – 1000psi. For CO2 cylinders, once the gauge reads in the red, the liquid gas is depleted and the cylinder should be refilled. The high pressure gauge does not represent the amount of liquid carbon dioxide in the tank. This measurement can only be determined by the weight of the tank less the tare weight (TW) of the tank; this determines the weight of liquid present. The tare weight is printed on the neck of the cylinder.

Low Pressure Gauge – located at the twelve o’clock position, it represents the working pressure or output pressure; the pressure you are using, which can be adjusted.

Adjustment Screw – Adjustments to the output pressure (read on the low pressure gauge) are made with the adjustment screw or knob located in the center of the regulator body. The output pressure is set by turning the screw clockwise to increase the output pressure. To reduce the output pressure, the screw should be turned completely counter clockwise, to vent pressure in the regulator, and then readjusted clockwise to the desired reduced pressure.

Tank Connector and Connector Nut – located at the three o’clock position, it attaches the regulator to the cylinder. Due to high pressure in the cylinder, this connection is a common location for leaks; it is critical to securely fasten the connector nut using the correct seal, nylon or permaseal. The connection must be tightened with a wrench.

Solenoid Valve – the solenoid valve is an electromechanical device that controls the flow of CO2 gas from the regulator to the aquarium. The solenoid should be connected to a timer or pH controller to control the input of CO2 into the aquarium. It is the on / off valve. The solenoid is typically mounted on the low pressure side of the regulator. The pressure in the solenoid will not get higher than the set output pressure of the regulator.

Pressure Relief Valve- functions to release excess pressure in the regulator.

Needle Valve – the most important part of the regulator. The needle valve provides precise control over the amount of CO2 allowed to enter the aquarium; it further reduces exit pressure of the regulator to approximately 1 – 3 psi. It allows you to fine tune and regulate the rate of flow (the number of CO2 bubbles per second) at the desired level. Not all needle valves, however, are created equal. It is important to invest in a quality needle valve for increased precision and to avoid the potentially negative effects of “end of tank dumps”. As the liquid gas in a cylinder nears empty, the pressure in the cylinder will decrease, causing the output pressure to quickly increase and potentially “dump” out of the cylinder into the aquarium. A needle valve will control this “dump” because it functions as the gateway that controls the volume of gas entering the aquarium, it will stabilize the increased output pressure at the set rate of flow (bubbles per second) preventing the CO2 from completely dumping into the aquarium.

Bubble Counter – a visual tool in measuring the number of bubbles per second entering the aquarium. A bubble counter allows you to count the exact number of bubbles per second so that fine adjustments can be made to the rate of flow.