Aquatic plants perform photosynthesis when light shines on their leaves. They use water and CO2 (carbon dioxide) as raw materials and produce glucose, oxygen and water through photosynthesis. Aquatic plants use the glucose to grow and release the oxygen, which is then used by fish and microorganisms for respiration. Among the raw materials for photosynthesis, water exists abundantly in an aquarium but CO2 may become deficient. CO2 is supplied to an aquarium by diffusion at the water surface and through the respiration of fish and microorganisms.
When a large number of aquatic plants are planted in an aquarium under a strong light, the plants consume CO2 rapidly through photosynthesis. This causes CO2 depletion and the plants stop photosynthesizing. If this condition persists, the aquatic plants cannot grow up healthy and dense. In Nature Aquarium, CO2 is injected into an aquarium to prevent this condition and to promote the photosynthesis of aquatic plants. If the volume of aquatic plants in an aquarium is small or the lighting is dim, it does not make sense to inject a large amount of CO2. On the other hand, if an entire aquarium is planted with aquatic plants and bright lighting is provided, sooner or later CO2 will be depleted. An adequate amount of CO2 needs to be injected into an aquarium in order to enable aquatic plants to perform photosynthesis smoothly.
The equipment necessary for a CO2 injection
A variety of methods have been devised to supply CO2 to an aquarium for many years. At present, a natural injection that is both safe and efficient has become the mainstream method. A cylinder of liquid carbon dioxide is used as the CO2 source. Since the cylinder is filled with CO2 at a high pressure, an aquarium CO2 regulator is use to discharge CO2 slowly.
The aquarium CO2 regulator is capable of depressurizing the compressed CO2 gas contained inside the cylinder and discharging it at a constant flow rate. The discharged CO2 goes through a ball valve that turns CO2 flow on and off and is then delivered to an aquarium using pressure resistant tubing. The pressure resistant tubing is connected to silicone tubing with a check valve. A glass CO2 diffuser and a glass counter, such as Pollen Glass and CO2 Glass Counter, are used to inject CO2 into the water in the aquarium. These glass components are both connected to the silicone tubing. CO2 Advanced System is a complete kit that contains all the necessary components for the CO2 injection. This set is designed for a 60 cm or a smaller aquarium. A 90 cm or a larger aquarium needs a system designed for a larger aquarium.
A cylinder selection
Small disposable cartridges and large refillable cylinders are available for the use with a CO2 injection system. Tropical Forest, which comes with the CO2 Advanced System, is a disposable cartridge. Although this 100 milliliter cartridge is small, it will last three to four weeks when used at the rate of one bubble per second using a CO2 Glass Counter for 8 to 10 hours a day, which is the proper amount for a 60 cm aquarium. Therefore, it is considered to be more suitable for an aquarium smaller than a 60 cm. A Tower/20 is more appropriate for a 90 cm or a larger aquarium. The capacity of a Tower/20 is 2 liters (equivalent of 20 disposable cartridges), which is more than adequate for a larger aquarium that requires a high injection volume. It is also compatible with a smaller aquarium such as a 60 cm aquarium. It enables you to inject CO2 without replacing CO2 cartridges for a long time and is quite economical as well. Although it requires a CO2 regulator designed for a larger system, it is well worth a consideration.
Pollen Glass selection
A difference between a CO2 injection system for a small aquarium and system for a large aquarium is the size of a Pollen Glass that diffuses CO2 in water. The sizes of Pollen Glass diffusers are determined by the diameter of the diffusion disc (white filter section). Pollen Glass and Pollen Glass TYPE-2 are the smallest diffusers designed for a 60 cm or a smaller aquarium. Pollen Glass Large 20 and 30, Pollen Glass Beetle 30, 40, and 50 are designed for progressively larger aquariums. As the size of the diffusion disc increases, the size of the aquarium that it is capable of supporting increases as well. For example, a diffuser with a 30 mm diameter disc is intended for a 90 cm aquarium, a diffuser with a 40 cm diameter disc is intended for a 120 cm aquarium, and a diffuser with a 50 mm diameter disc is intended for a 180 cm aquarium. As long as the diameter of the disc is the same, you can choose either a Pollen Glass Large or a Pollen Glass Beetle type diffuser based on the installation location and the design. Although a New Pollen Glass has the same size diffusion disc as a standard Pollen Glass, it looks sleeker, fitted with its own joint glass (supplied with the diffuser) and smaller suction cups. You can select either a Pollen Glass Large 30 or a Pollen Glass Beetle based on your preference on the design since they both have the same 30 cm diameter diffusion discs.
Installing a Drop Checker
A CO2 injection volume is measured by counting the number of CO2 bubbles using a CO2 Glass Counter (or a CO2 Beetle Counter for a large aquarium) and adjusted with a Speed Controller. The proper injection rate varies depending on the type and the denseness of the aquatic plants. A Drop Checker provides a good reference for determining if the CO2 injection volume is adequate or not. The pH of an aquarium that is planted with aquatic plants varies depending on a CO2 injection volume and the CO2 uptake level of the aquatic plants through photosynthesis. If the CO2 injection volume is high, the pH is more acidic. If it is low, the pH is more alkaline.
A Drop Checker is a CO2 detectors, a device that measures the CO2 concentration in an aquarium using this characteristic. It is installed inside an aquarium holding a small amount of the aquarium water and pH indicator in its glass bulb. CO2 injection volume is considered adequate if the color of the solution inside a Drop Checker looks blue (alkaline) in the morning when the light comes on, and appears green (slightly acidic) in four to five hours later when aquatic plants are photosynthesizing most vigorously. If the color remains blue, CO2 injection is insufficient. If it appears more yellow than green, it is excessive. The aquarium should be aerated at night when the light is turned off in order to prevent hypoxia.
A Drop Checker is an apparatus that indicates the CO2 concentration. It takes advantage of the characteristic that the pH of aquarium water comes to equilibrium with the pH of the water contained in the apparatus to which pH indicator is added via the air inside the apparatus. When CO2 dissolves in water, the pH of the water becomes acidic (the color of the solution turns yellow from green.) When CO2 is dispersed out of the water, pH becomes alkaline (the color of the solution turns blue.)
Pollen Glass maintenance
A Pollen Glass is a device that ultimately diffuses CO2 in water. The white diffusion disc of a Pollen Glass is a special glass filter with very fine openings, which releases CO2 into the water in the form of minute bubbles. These tiny bubbles dissolve in water while drifting in the current inside an aquarium or rising toward the water surface. Since a Pollen Glass is always submerged in an aquarium, algae will grow on its surface and sooner or later it will start to appear unsightly just like any glass surface or a rock and other composition materials. In the case of a Pollen Glass, algae on it not only appear unsightly but can also clog the diffusion disc and cause the bubble size to increase, resulting in poor diffusion efficiency.
The great advantage of Pollen Glass diffusers is that they are entirely made of glass. Glass is resistant against strong acids and alkalis and does not degrade over time. Therefore, algae on a Pollen Glass can be removed easily by soaking the diffuser in the alkaline cleanser Superge that is made for this purpose. A Pollen Glass can be used in a nearly new condition indefinitely. Cleaning a Pollen Glass once a week or every two weeks is recommended for maintaining the optimum diffusion capability.
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