Most of us remember being taught about photosynthesis at school, even if we don’t remember the finer details.

Allow me to give you a very quick reminder.  In plants, photosynthesis is a process of chemical reactions to make food from light, carbon dioxide (CO2) and water.  Aquatic plants, like any other plants, use photosynthesis to survive.

In an aquarium, plants can absorb only the CO2 that is dissolved in the water.  The more heavily planted the aquarium is, the more demand on the CO2 within the water.  If there is insufficient CO2 available inside the aquarium, plant growth and health will be severely affected.  Adding more CO2 to aquarium water will usually greatly increase the plant growth.

There are three methods of adding CO2 to aquarium water.

  • CO2 Bio-Systems – A basic system using a container, or bottle, with water, sugar, pH buffer and small amounts of yeast. These ingredients naturally ferment producing CO2 , which is dissolved into the aquarium water by a tube from with the CO2 bubbles.
  • CO2 Mechanical-Systems – These systems use a bottle of CO2 gas which is fed into the aquarium. Because of the more controlled nature of these systems, they usually come with valves that allow you to adjust the flow of CO2 into the aquarium water.
  • CO2 Electrolysis-Systems – Theses systems use electricity to convert a carbon block into CO2 gas, which slowly bubbles off the surface of the carbon block and dissolves into the aquarium water. Again, the flow of CO2 gas into the aquarium water can be adjusted as required.

With CO2 systems it is important to remember that too much CO2 in the water can be stressful to fish.  As photosynthesis only happens in the light, remember to switch off CO2 systems at the same time as the lights.  This, as well as managing the flow rate of the gas during the day, will ensure that there is only as much CO2 gas in the water as the aquarium needs to be healthy.

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