CO2 injection

CO2 injection means adding carbon dioxide gas into an aquarium's water so plants have enough of it to photosynthesize at a higher rate than the small amount naturally dissolved from the air. Since carbon dioxide is often the limiting factor in a heavily planted tank, injecting it allows denser growth, stronger color and more demanding carpeting and stem plants than a low-tech setup can usually support.

A typical setup uses a pressurized CO2 tank connected to a regulator that controls gas pressure, a solenoid valve that can be timed to run only during the photoperiod, and a diffuser or reactor that breaks the gas into fine bubbles the water can absorb. Getting the dosing right matters, because too little CO2 limits growth just as much as no injection at all, while too much can stress or kill fish and shrimp overnight, especially if it is added without a drop checker or timer to control it.

New CO2 users should introduce it gradually, watching fish behavior at the surface and checking a drop checker daily until the routine feels predictable, then keep the CO2 running only during the light period rather than around the clock. A common mistake is increasing CO2 to chase faster plant growth without also increasing light and fertilizer proportionally, which throws off the balance between the three and tends to trigger algae instead of the growth the extra CO2 was meant to produce.