A Closer Look at the CO2 Regulator, as it relates to the Planted Aquarium

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 is 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 1-40 PSI. Our 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.

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 t-handle 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.

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 crescent wrench or CO2 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 – one of the most important parts of the regulator. The needle valve provides precise control over the amount of CO2 allowed to enter the aquarium. 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.

The CAL AQUA “Oracle” and “Double-Check” – two exceptional drop checkers

With all of the advancements in drop checkers these days, it is becoming evident that not all drop checkers are created equally.  CAL AQUA LABS has taken the concept of the drop checker and expanded upon it to create the innovative “Oracle” and “Double Check” Drop Checkers.  These drop checkers are designed to meet and exceed the highest standards of quality in CO2 glassware, while enhancing the ease of use.  It is this ease of use that makes these two drop checkers exceptional.

The CAL AQUA “Oracle” Drop Checker

Unique to the “Oracle” is a small white column at the center of the solution chamber.  This column provides a white background for definitive color contrast and precise color identification when observing the solution color in the checker.  In a standard drop checker it can be a difficult task to make an accurate judgement of the solution color if the checker is placed against a dark background or in front of plants; this can affect precise measurement of CO2 concentration in the aquarium water.

Also unique to the “Oracle is a wide neck for easier filling of the indicator solution.  The increased width of the reservoir creates a wider air-water interface which allows for a faster response time in the change of the solution color.

The CAL AQUA “Double Check” Drop Checker

The “Double Check” is the first all-glass dual-compartment drop checker that allows the user to accurately compare, side-by-side, the CO2 level in one’s planted aquarium against an optimal CO2 concentration, indicated by a standard green reference solution.  It is designed to be efficient and accurate, implementing a simple visual comparison of the indicator solution and a standard reference solution. The reference solution is simply a green reference color that represents the optimal level of CO2 in the aquarium.  When compared with the indicator solution color, the optimal level of co2 can be determined and achieved.

Check out our selection of CO2 drop checkers at our webstore, Green Leaf Aquariums.  We hope that you will find the perfect one for your needs.

The Drop Checker – How to & the Science behind it

1. Preparation of Indicator Solution:

The correct indicator solution is a combination of KH Standard / 4 degree KH (4 dKH) and pH indicator (Bromothymol Blue).

With drop checker in hand, turn upside down and fill the reservoir of the drop checker approximately half full (or to level manufacturer recommends) with 4 dKH.  A syringe is an ideal tool to use for this.  Then, add approximately 2 – 4 drops of pH indicator (Bromothymol Blue) until a strong, TRANSPARENT blue color is achieved.

The Science:

pH and pH IndicatorpH is a measure of the acidity or alkalinity of a solution. pH indicator is a chemical detector that causes the color of the solution to change depending on pH.

KH and KH StandardKH (Carbonate Hardness) is the measurement in degrees of carbonate and bicarbonate in the water.  KH Standard is a solution with a known KH, a standard, with no other buffers other than carbonate and bicarbonates.

To measure CO2 in the aquarium, you need to have an accurate measurement of KH and pH.  With a known value of KH / carbonate hardness in the indicator solution, the color of the solution will turn green when the optimal concentration of 30 ppm of CO2 is achieved in the aquarium water.  A yellow or blue color indicates too much or too little CO2 in the water, respectively.


2. Place in Aquarium and wait to observe color change:

With the correct side up, place the drop checker in the aquarium, in a visible location.  After approximately one hour, you should notice a change in the color of the indicator solution.  After about two (2) hours you should be able to observe the color and take an accurate measurement of the concentration of CO2 in the aquarium.  For increased accuracy it is recommended to observe the color against a solid white background.

BLUE ->  too little CO2 / low CO2 levels  ->  increase the rate of CO2

GREEN ->  proper CO2 levels  ->  no action required

YELLOW ->  too much CO2 / high CO2 levels  ->  decrease the rate of CO2


The Science:

The drop checker is a reservoir designed to contain an indicator solution and an airspace or air bubble.  When submerged in an aquarium, the airspace eliminates contact between the indicator solution and the aquarium water.

When CO2 is injected into the aquarium, the CO2 will out gas from the aquarium water into the airspace of the drop checker.  As CO2 enters the air, it is absorbed into the indicator solution.  The absorption of CO2 is the result of the gas seeking a point of equilibrium, or equal distribution of CO2 in the solution and the air; the basic principle behind the function of the drop checker.  As CO2 gas is absorbed into the indicator solution, it lowers the pH of the KH standard, which in turn changes the color of the pH indicator.  This condition of equilibrium allows the drop checker, a simple glass reservoir, to provide a highly accurate measurement of carbon dioxide (CO2) in the planted aquarium.

This process is reversed when the injection of CO2 is decreased or zeroed, and the indicator solution contains more CO2 than the aquarium water.  The CO2 will outgas from the indicator solution to seek equilibrium with the airspace and the aquarium water.  This out gassing of CO2 will raise the pH of the solution and change the color of the pH indicator.

In summary, never underestimate the power of the drop checker as an accurate tool for the measurement of CO2 (when used correctly).  Look forward to a video to follow.