Why is CO2 injection necessary?
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.