CO2 supply is effective for growing healthy and beautiful aquatic plants in an aquarium. Particularly, the growth rate of sun plants such as stem plants and many foreground plant species, greatly differ depending on the implementation of CO2 supply. However, aquatic plants do not show healthy growth if CO2 is simply added to the aquarium. In an aquarium to which CO2 is supplied, a good balance with illumination level and nutrients must be maintained as an important element.


■Why CO2 needs to be supplied to an aquarium?

Aquatic plants, which are green plants, grow by performing photosynthesis to produce organic compounds. In order to undergo photosynthesis, plants need light, water and carbon dioxide (CO2). Aquatic plants that perform photosynthesis underwater use abundant water around them and blue light that penetrates easily in water. At the same time, aquatic plants use CO2 in the air that has dissolved into water (CO2 easily dissolves into water) or released by fish and other animals in their breathing process. If the aquarium tank has too little water for the amount of aquatic plants in it, the CO2 dissolved into the water or released by animals is easily consumed and runs out very fast, which leads to chronic lack of CO2 in the aquarium. The rate of photosynthesis increases in proportion to the light intensity to a certain level; and therefore, CO2 becomes scarce immediately after the light is turned on and aquatic plants stop photosynthesis particularly in planted aquarium with bright lighting system installed. For such an aquarium, insufficient CO2 level can also be found by the change in water quality. When an aquarium is filled with ordinary freshwater near neutral pH (pH 7.0), its pH level increases as CO2 in the water is used for photosynthesis and becomes scarce and the water will eventually turn to alkaline (around pH 8.0). In this condition, aquatic plants cannot perform adequate photosynthesis and their growth will be significantly affected. In order to improve this problem and ensure healthy growth of aquatic plants, CO2 supply is required in Nature Aquarium.



■Basic CO2 System

After trying various methods to find optimal CO2 supply for Nature Aquarium, the natural supply of CO2 using a cartridge filled with liquefied carbon dioxide was selected as an established method. Natural supply of CO2 means to diffuse fine bubbles of highly pure CO2 gas and dissolve them into water. Fine CO2 bubbles are used for this purpose because they have a larger surface area as compared to the same amount of CO2 gas bubbles and hence, they are readily dissolved into water. An essential item for this natural supply of CO2 is the Pollen Glass series. Pollen Glass makes fine CO2 bubbles by letting CO2 gas into its very fine mesh filter and diffuses them into water. Please be reminded that it is ideal to add CO2 to an aquarium at an amount just sufficient for aquatic plants to perform photosynthesis. An excessive amount of CO2 can create a risk of causing lack of oxygen to fish, shrimp and living organisms in the aquarium. To prevent this problem, it is recommended to count CO2 bubbles with CO2 Bubble Counter and regulate the CO2 amount with Speed Controller. CO2 Advanced System is a basic CO2 system designed for 60cm or smaller aquarium tanks. It includes all the equipment and parts necessary for supplying CO2 to planted aquarium, such as Pollen Glass, CO2 Glass Counter, CO2 Regulator (YA/Ver.2) and 74g small CO2 cartridge (Tropical Forest, etc.).



■ For More Effective CO2 Supply

CO2 Advanced System is not suitable for 90cm or larger aquarium tanks. For large aquarium tanks that contain a large volume of water thus requiring more CO2 to be supplied, Pollen Glass Large (20Ø or 30Ø) and Pollen Glass Beetle (30Ø, 40Ø or 50Ø), a CO2 diffuser designed for large aquarium tanks should be used in combination with CO2 Beetle Counter that caters for the measurement of larger amounts of CO2. For the CO2 tank and regulator, CO2 tank Tower and CO2 Attache Regulator designed for the use with Tower should be used for this size of tanks. Building a CO2 system designed for large aquarium tanks enables more efficient CO2 supply.




With CO2 supply (after 1 week)


No CO2 supply (after 1 week)


Difference in aquatic plant growth between Tank (A) with CO2 supply and Tank (B) with no CO2 supply. Apparently, aquatic plants in the tank with CO2 supply grow better and show vivid colors.





What is the tip of CO2 Advanced System?



If you think of starting planted aquarium hobby with a 60cm tank and trying a larger tank later, or if you wish to use a larger CO2 tank even for 60cm aquarium tank, it is recommended to use CO2 Advanced System from the beginning because CO2 Regulator (YA/Ver.2) included in CO2 Advanced System can be connected to Tower designed for larger aquarium tanks with the use of CO2 Adapter (accessory).


Green Bacter, which is effective for aquarium in its initial set up period, is contained in Advanced System.





The leaf color of my aquatic plants looks faded. Am I supplying too little CO2 to my aquarium?


To determine whether an appropriate amount of CO2 is supplied to your planted aquarium, you can install Drop Checker in the tank. If the aquarium water is neutral (near pH7.0) and aeration is performed during the night while the light is turned off, the water turns to neutral to mild alkaline in the morning. At this time, the reagent of Drop Checker is bluish green. Then you start supplying CO2 to the tank and if the reagent is green, which indicates that the water is mildly acidic, after 4-5 hours, the CO2 amount is appropriate. If the reagent is blue, which indicates alkaline, or yellow, which tells you acidic water quality, instead of green, CO2 supply is insufficient or excessive, respectively. If the leaf color is not vibrant even when an appropriate amount of CO2 is supplied, you can suspect lack of nutrients such as nitrogen and iron. In this case, add Green Brighty Special LIGHTS (contains rich nitrogen) or ECA (contains rich iron) to the aquarium, in addition to basic liquid fertilizers Brighty K and Green Brighty STEP2, to improve leaf color.



Insufficient CO2


Appropriate CO2 amount


Excessive CO2


Drop Checker measures CO2 concentration by the change of reagent color.

Blue (top), green (middle) and yellow (bottom) show insufficient CO2, appropriate CO2 amount and excessive CO2, respectively.



Green Brighty Special LIGHTS is a liquid fertilizer specifically designed for sun plants such as stem plants.


(From Aqua Journal #243)