Tetra Test CO2 measures the carbon dioxide value reliably and precisely. Just like fish, plants also breathe by absorbing oxygen (O2) and emitting carbon dioxide (CO2). Under the influence of light, however, plants can carry out a process, which is known as photosynthesis. During photosynthesis, CO2 is absorbed (as food) and O2 is emitted. For this reason, plants require a constant supply of CO2 to ensure their strong and healthy growth. Good ventilation, e.g. using an air stone, ensures that your fish receive a plentiful supply of oxygen, but at the same time reduces the CO2 concentration, thus minimizing the most essential form of nutrition for your aquatic plants. By regularly controlling the CO2 values, you can ensure that sufficient carbon dioxide is available for healthy plant growth.The following values are guidelines for CO2 concentrations in ventilated aquaria: 1. A CO2 concentration of between 0.5 and 1 mg/l is too low for rich plant growth. 2. Long-term values of between 5 a