When fish consume oxygen, CO₂ is released in the water. To high carbon dioxide levels can negatively influence the fish growth or even be lethal. Therefore, it is important that CO₂ is efficiently removed from the culture water. Degassing towers or active aeration are two principles, which are commonly used in aquaculture. Both methods are based on diffusion of CO₂  out of the water into air.

When a large fraction of the CO₂  must be removed from the water then the most efficient tool is the degassing tower, basically a low-height trickling filter. If higher concentrations of CO₂ are tolerated diffuser aeration may be the most efficient tool.