The Anubias genus, including popular varieties like Anubias barteri and Anubias nana, consists of extremely hardy, slow-growing aquatic plants originating from tropical West Africa. They are a staple in the aquarium hobby due to their distinctive thick, leathery leaves and ease of care. A frequent question among new aquarists concerns whether supplemental carbon dioxide (\(\text{CO}_2\)) injection is necessary for their survival and health.
Answering the Necessity Question
The direct answer to whether Anubias requires supplemental \(\text{CO}_2\) injection is no; it is not necessary for the plant to survive or grow. This genus is tolerant of low-tech aquarium environments, thriving with only the ambient \(\text{CO}_2\) naturally present in the water. The \(\text{CO}_2\) dissolved from the air and produced by fish respiration is generally sufficient to meet the plant’s metabolic demands. This low-demand profile makes Anubias consistently recommended for beginners.
Its reputation as one of the most forgiving aquarium plants is linked to its slow growth rate. Since the plant has a low metabolism, it requires a smaller and steadier supply of carbon compared to faster-growing stem plants. It can successfully grow a new leaf approximately every three to six weeks in a non-\(\text{CO}_2\) environment. This characteristic allows the plant to maintain health and even propagate slowly.
Alternative Carbon Acquisition
The ability of Anubias to thrive without injected \(\text{CO}_2\) is related to a biological adaptation common among certain aquatic species. While plants prefer gaseous \(\text{CO}_2\) for photosynthesis, its concentration in water can be limiting, especially in tanks with higher \(\text{pH}\) and alkalinity. Many aquatic macrophytes have evolved the capability to utilize bicarbonate ions (\(\text{HCO}_3^-\)) as an alternative carbon source.
Bicarbonate is the predominant form of inorganic carbon in water with moderate to high carbonate hardness (\(\text{KH}\)). Plants that can use this ion employ a process, sometimes referred to as Bicarbonate Use, to convert the \(\text{HCO}_3^-\) into a usable form. This conversion often involves enzymes or specialized transport mechanisms on the leaf surface. This adaptation minimizes the plant’s reliance on fluctuating levels of dissolved \(\text{CO}_2\) gas, allowing it to sustain its slow but steady growth.
Essential Growth Factors
Since supplemental carbon is not a requirement, the health of Anubias depends far more on other environmental factors. The plant performs best under low to moderate lighting, which is sufficient for its slow photosynthetic rate. Lighting that is too intense can be detrimental, as the slow-growing leaves become susceptible to algae growth. A photoperiod of eight to ten hours per day with low light intensity is optimal for preventing algae accumulation.
The plant’s nutrition is primarily absorbed from the water column, unlike many rooted plants. While it can survive on nutrients from fish waste, regular dosing of a comprehensive liquid fertilizer ensures optimal health. This fertilizer should contain micronutrients, such as iron, and macronutrients, like potassium and nitrogen. It is necessary to ensure the thick horizontal stem, or rhizome, remains exposed to the water and is not buried in the substrate.
Burying the rhizome is a common mistake that will cause it to rot, leading to the eventual death of the plant. Anubias naturally anchors itself to rocks or driftwood using its fine roots. Adequate water flow around the plant is beneficial, as it helps deliver nutrients directly to the leaves and disperses metabolic waste products. This movement helps reduce the risk of algae settling and establishing colonies on the leaf surfaces.
Effects of Supplemental \(\text{CO}_2\)
Although Anubias does not require \(\text{CO}_2\) for survival, introducing it will accelerate the growth rate. In a high-tech setup, the plant’s metabolism is increased, potentially reducing the time between new leaf growth from several weeks to just two weeks. This results in a bushier, denser plant with fuller leaves.
This increased growth must be supported by a proportional increase in both light and nutrients. If \(\text{CO}_2\) is added without increasing light and fertilizer levels, the plant cannot properly utilize the extra carbon and may suffer nutrient deficiencies. The slow-growing nature of Anubias makes it a target for algae in high-energy tanks. If the balance of light, nutrients, and \(\text{CO}_2\) is not maintained, fast-growing algae will quickly colonize the leaves, which are difficult to remove without damaging the plant.